feat(base)!: no anonymous accounts on the server (ADR 0020, D25)

The server's half of D25: every account has a way in, and the anonymous
accounts left from before go with the daily pruning.

- The module signs nobody in anonymously: `anonymousIdp` and
  `gitHubUpgrade` are gone, and so is linking GitHub at the register.
- A password is set only by someone whose address is theirs (a
  `firstPassword` code) or who signs in with GitHub alone (a fresh
  sign-in and a `signUp` code); an anonymous account is refused
  `wrongCredentials` before any code is used.
- SimpleLogin refuses to link onto a caller without `identified`
  (`wrongCaller`), the member's endpoint too, so nothing turns an
  anonymous account into one with a way in.
- `pruneAnonymousPeople` deletes every anonymous account left, however
  new, never one identified. Learn and Todo schedule it as
  `prune-accounts` and cancel the old `prune-abandoned-anonymous-people`
  entry once.
- Learn: someone without `identified` keeps no files;
  `FILE_LIMIT_ANONYMOUS_MB` is gone. `minimumAppBuild` is 23, as builds
  up to 22 start with an anonymous account.
- Learn's sync tests make their person and session by SQL in the
  development database, as Serverpod stores sessions.
- Docs, store listings and ADRs 0010, 0014, 0016, 0017 and 0019 amended.

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

deploy/compose.yaml

@@ -92,7 +92,7 @@ services:
       # The ways in offered, of those set up (`simplelogin password`); empty: all.
       SIGN_IN_WAYS: ${SIGN_IN_WAYS:-}
       # Caddy, whose X-Forwarded-For names the visitor the per-network limits count
-      # (new anonymous accounts, codes by mail, password sign-ins): without it, every
+      # (codes by mail, password and SimpleLogin sign-ins): without it, every
       # visitor would share each limit with everyone. Its address on `edge`, below.
       TRUSTED_PROXIES: 172.30.80.2 fd4a:6c6b:7e80::2
       # The day GitHub stops signing anyone in (`2027-01-22`); empty: no end.
@@ -115,7 +115,6 @@ services:
       DATA_LOCATION: ${DATA_LOCATION:-}
       BACKUP_LOCATION: ${BACKUP_LOCATION:-}
       # How much room people's files may take, in MiB; empty: the defaults.
-      FILE_LIMIT_ANONYMOUS_MB: ${FILE_LIMIT_ANONYMOUS_MB:-}
       FILE_LIMIT_IDENTIFIED_MB: ${FILE_LIMIT_IDENTIFIED_MB:-}
       FILE_LIMIT_INSTANCE_MB: ${FILE_LIMIT_INSTANCE_MB:-}
       # The git repositories of published studysets (ADR 0005, rule 3).