review follow-up: close the gaps left by the phase1-6 pass

Verified the tree against docs/plans/code-review-2026-08.md and finished the
tasks that were only partly done, plus two defects the pass introduced.

- bcrypt: the setup account was still hashed at DefaultCost (10). The work
  factor now has one definition, auth.BcryptCost = 12, used everywhere.
- rate limiter: protecting blocked buckets from eviction was unbounded — an
  attacker with many source addresses could grow the map by making each one
  fail its way to blocked. Blocked buckets are now evicted past
  maxBuckets * 4, nearest expiry first, logged once per window. Tests cover
  both halves.
- postqueue: the 5s timeout left the output size unbounded; reads are now
  capped at 4 MiB and report truncation.
- spec references: the ~76 `spec N` citations CHANGELOG [0.5.0] claimed were
  gone are removed from build/, deploy/, the first two migrations and the
  release workflow, with the affected comment paragraphs re-wrapped. Comments
  only; shell/YAML/SQL syntax re-checked.
- schema-migrations.md: schema section was headed v9 with the chain at v10,
  and three links pointed at deleted plan files.
- internal/configsafe: the shared empty/forbidden-character check behind the
  OpenDKIM and Postfix config writers; each writer keeps its own forbidden set.
- dropped the parseDomainRateLimitForm/parseAppRateLimitForm pass-throughs
  left behind by the parser merge (only their own tests still called them).
- plan doc now carries a status table: what shipped, what was already in
  place, what was declined (//go:build linux for the /proc reader) and the
  open CSRF-token question.

Not done, each its own phase: typed template data structs, log/slog, DMARC
service and handler tests, error-page/corrupted-backup tests, backup re-auth.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

build/supervisord.conf

@@ -1,4 +1,4 @@
-; SelfPost process supervision (spec 4).
+; SelfPost process supervision.
 ;
 ; Start ORDER is enforced by priority=: OpenDKIM, then the panel (which opens
 ; the journal-milter socket), then the Postfix wrapper — which additionally
@@ -18,8 +18,8 @@ loglevel=info
 
 ; The control socket is reachable by the shared `selfpost` group so the panel
 ; (running as the unprivileged `panel` user) can ask supervisord to send
-; OpenDKIM a reload signal after it rewrites the DKIM tables (spec 6.2). It is
-; still unreachable by world; only root and the two SelfPost services are in the
+; OpenDKIM a reload signal after it rewrites the DKIM tables. It is still
+; unreachable by world; only root and the two SelfPost services are in the
 ; group. No HTTP auth is configured because access is gated by socket
 ; permissions, not the network.
 [unix_http_server]
@@ -67,15 +67,15 @@ stdout_logfile_maxbytes=0
 stderr_logfile=/dev/stderr
 stderr_logfile_maxbytes=0
 
-; One-shot reload helper (spec 5.2, 7.2.12). The panel runs unprivileged and
-; cannot run `postfix reload` itself, and it cannot signal the Postfix master
-; directly: `postfix start-fg` forks a separate master process, so a signal to
-; the supervised foreground process never reaches it (unlike OpenDKIM, which
-; runs in the foreground as the supervised process itself). Instead the panel
-; asks supervisord — over the group-accessible control socket — to run this
-; program, which executes the canonical `postfix reload` as root. autostart is
-; off (it only runs on demand) and a fast, clean exit is expected, so it never
-; trips the crashexit listener.
+; One-shot reload helper. The panel runs unprivileged and cannot run `postfix
+; reload` itself, and it cannot signal the Postfix master directly: `postfix
+; start-fg` forks a separate master process, so a signal to the supervised
+; foreground process never reaches it (unlike OpenDKIM, which runs in the
+; foreground as the supervised process itself). Instead the panel asks
+; supervisord — over the group-accessible control socket — to run this program,
+; which executes the canonical `postfix reload` as root. autostart is off (it
+; only runs on demand) and a fast, clean exit is expected, so it never trips the
+; crashexit listener.
 [program:postfix-reload]
 command=/usr/sbin/postfix reload
 autostart=false
@@ -88,7 +88,7 @@ stdout_logfile_maxbytes=0
 stderr_logfile=/dev/stderr
 stderr_logfile_maxbytes=0
 
-; Periodic TLS-certificate refresh (spec 5.2 p.4). Runs a daily `postfix reload`
+; Periodic TLS-certificate refresh. Runs a daily `postfix reload`
 ; so certificates the reverse-proxy renews in the read-only mount are picked up.
 ; Long-running (it loops), runs as root so it can reload Postfix, and never exits
 ; non-zero, so it neither trips the crashexit listener nor needs restarting.
@@ -103,10 +103,10 @@ stdout_logfile_maxbytes=0
 stderr_logfile=/dev/stderr
 stderr_logfile_maxbytes=0
 
-; Periodic logrotate for /data/log/mail.log (spec 9, 10: daily, 7-14 files kept
-; in the image). Runs as root so logrotate can read/rotate the log. Exits
-; non-zero when the config is group/other-writable (logrotate would ignore it
-; silently); autorestart surfaces BACKOFF on the Status page.
+; Periodic logrotate for /data/log/mail.log (daily, 7-14 files kept in the
+; image). Runs as root so logrotate can read/rotate the log. Exits non-zero when
+; the config is group/other-writable (logrotate would ignore it silently);
+; autorestart surfaces BACKOFF on the Status page.
 [program:logrotate]
 command=/usr/local/bin/logrotate-loop.sh
 priority=400