fix(auth): count per-network limits by the visitor behind Caddy

Every per-network limit counted by the connection's address, which behind
Caddy is Caddy's for everyone: new anonymous accounts, codes by mail and
password sign-ins were each limited for the whole instance.

`networkOf` (now `common/network.dart`) takes the last address of
X-Forwarded-For, the one the proxy saw itself, for a connection from a
proxy the operator trusts (`TRUSTED_PROXIES`, which deploy/compose.yaml
sets to Caddy's fixed address); otherwise, or where that is no address,
the connection's. Never the Forwarded header, which Caddy passes on as
sent, so never Serverpod's `remoteInfo`. A value that isn't addresses
stops the server as it starts.

Serverpod's own limit on anonymous accounts counts by the connection's
address too and can't be told otherwise, so it is off; the anonymous
endpoint counts them itself, 30 an hour per network as before.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

apps/learn/AGENTS.md

@@ -115,7 +115,7 @@ A spaced-repetition learning app: studysets of flashcards, reviewed on an FSRS s
 - **Reports and suggestions** (ADR 0005, stage 4, rule 11): `feedback_thread` (a report or suggestion: `publicationId` and `kind` columns, everything else in its payload: what it is about by release item id and version, a report's category, the text, a suggestion's proposed payload and the files it names), `feedback_message` (replies) and `feedback_decision` (an author's closed, reopened, hidden, shown, accepted, declined; the latest of each pair stands) are synced tables each person writes in their own space; a thread or reply names its thread by id only, as it may be another person's. `gatherFeedback` (`lib/src/feedback/`) assembles them for `FeedbackEndpoint.threadsOf` (`requireLogin`: public) and `InboxEndpoint` (`identified`: the inbox, unseen counts, `markSeen`, `block`, `file`) and decides what counts as it reads (see the ADR), since a modified app could write anything. `feedback_block` and `feedback_seen` are server-only; `deletePerson` deletes both. A release's commit credits the writers of suggestions accepted since the last (`Co-authored-by`). In the app (`feature/feedback/`): the card's Report sheet offers "Send to the author too" on a card from a release; a copy's ⋮ menu reports the studyset and lists its threads, as Explore's summary does; the editors of cards (⋮), notes and steps (app bar) suggest to the author (refused under "no derivatives"); the Inbox is in the Profile tab, with a count on the tab (`InboxCountBloc`, refreshed at start and whenever the inbox is read or acted on; no timer); a thread's sheet shows a suggestion beside the author's own item, its replies, and the author's decisions. Accepting writes the proposed content as the author's own revision (`FeedbackRepository.accept`), the writer's files fetched by hash.
 - **Discussions** (ADR 0013, decided 2026-10-15): questions on a published studyset, a topic in it or one of its cards, notes or steps, answered by anyone and commented on (under the question and each answer, never under a comment), as Stack Exchange has them, without votes: the asker accepts an answer, which comes first, the rest oldest first. Unlike feedback they are server tables (`discussion_post`, `discussion_seen`, `lib/src/discussion/`), written through endpoints, online only, so posts can be edited and ordered and the synced tables stay as they are: `DiscussionsEndpoint` (`requireLogin`) lists (by topic, item or title, 30 to a page, last active first) and reads; `DiscussionEndpoint` (`identified`, and a public profile) asks, answers, comments, edits, deletes, accepts, hides (the studyset's author), and keeps the inbox. A question names its target as the release does, and the instance keeps the topics it is within from git's file list (`ReleaseRepository.paths`, `topicsOf`), so a topic lists what is asked within it and below; one about the studyset as a whole names no item. Questions and answers are rich text without files (the composer's Insert menu has no media, and content holding images or sounds is refused: the person's files are theirs alone), comments plain text of up to 600 characters, 30 posts an hour. The author hides posts and blocks people with feedback's own blocks; a withdrawn studyset takes no new questions. A post with others' replies under it is never deleted, only emptied ("Deleted question"), with its writer's account too (`deleteDiscussionsOf` in `deletePerson`). In the app (`feature/discussion/`): a copy's menu opens the discussions within that studyset or topic (`RoutePaths.discussions`, over the tabs), a studied card from a release offers Ask about this, Explore's summary and the Publish sheet open the whole studyset's, and the Profile tab's inbox lists the discussions the person follows, counted on the tab with the feedback (`InboxCountBloc`).
 - **Deleting a person** goes through halkyon_base's `deletePerson`, in one transaction and in ADR 0001 rule 6's order: their sessions end first (a device with a valid session would re-upload everything), then Learn's own data of theirs (`deleteLearnData`, `lib/src/auth/account.dart`, the hook Learn configures: their space with all its content through the foreign keys and its stored files, discussions, published studysets, blocks, what they read, the assistants they connected, their file allowance; their releases' repositories once the deletion holds), then the module's (their public profile with its avatar), then the person with their identities; an identified person's deletion also tells the instance's members (ADR 0016), the notices kept in the same transaction. What they wrote in discussions goes too, emptied where others replied under it (ADR 0013). A new table holding a person's data gets a line in that hook. The module's `account.delete` deletes the caller; the app also calls it when an anonymous account is given up (signed out of, or switched away from to GitHub), since nobody could ever sign into it again.
-- **Pruning**: `PruningFutureCall` (Learn's, calling halkyon_base's functions; people go through its `deletePerson`, so Learn's data of theirs too) deletes anonymous people unused for 90 days, daily, scheduled when the server starts; and hourly the notes Serverpod's rate limit makes of anonymous sign-ups (`serverpod_auth_idp_rate_limited_request_attempt`, each with the IP address it came from) once the limit's hour is past (`forgetOldSignUpAttempts`; email sign-in's notes too, and its codes past their time, `forgetExpiredEmailCodes`): Serverpod deletes them only for its own email sign-in, which this instance doesn't use, so they would otherwise stay for good, and the privacy page says the instance keeps no IP addresses beyond that; hourly too, the deletions the instance's members haven't confirmed yet (`tellMembersOfDeletions`, ADR 0016). Scheduling a future call always adds an entry, so the server cancels the previous one by its identifier first.
+- **Pruning**: `PruningFutureCall` (Learn's, calling halkyon_base's functions; people go through its `deletePerson`, so Learn's data of theirs too) deletes anonymous people unused for 90 days, daily, scheduled when the server starts; and hourly the notes the rate limits make (`serverpod_auth_idp_rate_limited_request_attempt`; anonymous sign-ups, codes by mail and password sign-ins are counted per network, each note keyed by the visitor's IP address: `networkOf`, which behind Caddy reads the last address of `X-Forwarded-For` from the proxies `TRUSTED_PROXIES` names, as `deploy/compose.yaml` names Caddy, never the `Forwarded` header) once the limit's hour is past (`forgetOldSignUpAttempts`; email sign-in's notes too, and its codes past their time, `forgetExpiredEmailCodes`): Serverpod deletes them only for its own email sign-in, which this instance doesn't use, so they would otherwise stay for good, and the privacy page says the instance keeps no IP addresses beyond that; hourly too, the deletions the instance's members haven't confirmed yet (`tellMembersOfDeletions`, ADR 0016). Scheduling a future call always adds an entry, so the server cancels the previous one by its identifier first.
 - **Coming back with a field focused brings its keyboard back** (`KeyboardBackOnResume` around the app): Flutter (v3.47.5) gives the window back the keyboard's height after the app was left while the keyboard moved, with no keyboard showing, which left screens pushed up ([flutter#191156](https://github.com/flutter/flutter/issues/191156), open). Remove it once that is fixed.
 - **One person's data per device**: `PersonFolders` wipes every other person's folder when a person's data opens: their sessions ended on this device. Opening waits for the previous person's database to close.
 - **Session logs are not persisted** (`persistentEnabled: false` in every run mode) for privacy. Don't re-enable them.