feat(base,learn): suggest changes within a shared studyset

ADR 0044's step 6b (D44, D46 to D48): a Viewer, and an agent, suggest
changes within a shared studyset, which its Owner and Editors accept or
decline.

A suggestion or report is written as Explore's are, in its writer's own
synced space, with kinds of its own (space-suggestion, space-report)
and the space's id in feedback_thread's publicationId, so no synced
table changes and older apps, skipping kinds they don't know, keep
syncing. Where the studyset is private it is sealed with its key, bound
to the space; a reply to it is sealed for its thread.

Learn's server gathers a space's threads for its members alone
(feedback.threadsInSpace, NotFound for anyone else): only threads and
replies by members now, decisions only from rows in the space itself,
where the engine lets its Owner and Editors alone write; sealed
payloads pass in base64 with their key and nonce. The inbox adds the
threads its caller decides on or wrote. The module tells a host a
person's spaces and each space's members (sharedSpacesOf,
membersOfSpaces). No migration: no table changes.

In the app, a Viewer's card and note offer Suggest a change: the fields
write into the suggestion alone, sent with a message. A shared
studyset's menu lists its Suggestions, where its Owner and Editors
accept a change as a revision, or a new card or note into the
studyset, and decide in the space. A suggestion naming a file that
isn't the studyset's, or bringing files of its own, isn't taken.

Whats-New: In a studyset shared with you as a viewer, suggest a change to a card or note; its owner and editors find your suggestions under Suggestions in its menu and accept or decline them.
Whats-New-De: In einem Lernset, das du nur ansehen darfst, schlägst du Änderungen an Karteikarten und Notizen vor; Besitzer:in und Bearbeiter:innen finden sie im Menü unter „Vorschläge“ und nehmen sie an oder lehnen sie ab.

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

docs/adr/0044-shared-spaces-and-collaboration.md

@@ -6,7 +6,7 @@
   agent's recommendations, which they chose on 11 Nov 2026, D14 too, and D15 to D26;
   D27 their choice; D28 the agent's, to be confirmed; D29 to D32 the agent's
   recommendations, which they chose.
-  Steps 1 to 5 and step 6's first part built; the rest below.
+  Steps 1 to 5 and step 6's first two parts built; the rest below.
 - **Builds on:** ADR 0005 (publishing, reports and suggestions), ADR 0014 (the module),
   ADR 0016 (one account across an instance), ADR 0017 (key pairs), ADR 0019 (private
   studysets), ADR 0021 (operators and assistants).
@@ -250,6 +250,24 @@ member reads everything in the space.
   and signs in no other way. It sets its public keys itself, once. Deleting the owner
   deletes their agents first, as accounts are deleted; its public profile says whose
   agent it is.
+- **D46.** **A suggestion in a shared space is kept as Explore's are** (decided 11 Nov
+  2026, the agent's recommendation): in its writer's own synced space, so it is written
+  offline, sealed with the shared studyset's key where that is private; the instance
+  gathers each space's for its members, checking membership and role as it reads.
+  `feedback_thread` takes it as kinds of its own (`space-suggestion`, `space-report`),
+  its `publicationId` holding the space's id, so no synced table changes and older apps,
+  skipping kinds they don't know, keep syncing. Editors' and the Owner's decisions are
+  written into the shared space itself, where the engine already allows them alone.
+  Over rows of the shared space written by Viewers, which would need the engine to let
+  a read-only member write some tables.
+- **D47.** **Every member sees them** (decided 11 Nov 2026, the agent's recommendation):
+  a suggestion or report in a shared space, and its replies, show to everyone in it,
+  Viewers too, as Explore's show to everyone learning a studyset.
+- **D48.** **Changes and new items** (decided 11 Nov 2026, the agent's
+  recommendation): a Viewer or an agent suggests a changed card, note or step, as on
+  Explore, and new cards and notes for the studyset or one of its topics; deleting is
+  asked for with a report. A suggestion may name the files the studyset holds; new
+  files it would bring come later.
 
 ## Steps
 
@@ -313,7 +331,22 @@ member reads everything in the space.
       once to copy, new token, taken back, deleted) and members marked as agents
       (`SpaceMember.agent`; Learn's Share sheet: a bot, "Agent", no role above
       Viewer offered, none to hand the studyset on to).
-   b. Suggestions within a shared space (D10, D44).
+   b. **Suggestions within a shared space** (D10, D44, D46 to D48), built 11 Nov
+      2026: Learn's `feedback.threadsInSpace` gathers a space's threads
+      (`space-suggestion`, `space-report`) for its members alone, its writers
+      and repliers members now, its decisions read from the space's own rows;
+      the inbox adds those the caller decides on or wrote; a sealed payload
+      passes in base64 with its key and nonce (`FeedbackView.space`, `keyId`,
+      `nonce`). The module tells a host a person's spaces and each space's
+      members (`sharedSpacesOf`, `membersOfSpaces`). In the app,
+      `FeedbackRepository` suggests changed cards, notes and steps and new
+      cards and notes, reports, replies (sealed for their thread) and decides
+      in the space (`SpaceRouter.placeRow`), and takes a suggestion in only
+      where it names the studyset's own files and brings none; a Viewer's
+      card and note offer Suggest a change, and a shared studyset's menu its
+      Suggestions, where its Owner and Editors accept or decline. New cards
+      and notes are suggested through the repository (the agent, step 6c);
+      the app offers a Viewer no button for them yet.
    c. The agent itself, its CLI and MCP server, on a pure-Dart core (D7, D41).
 
 ## Open questions, before building