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>

deploy/traefik/docker-compose.traefik.yml

@@ -1,7 +1,7 @@
 
-# Alternative reverse-proxy: Traefik (spec 10.3). Traefik does NOT write plain
-# PEM files — everything (cert + key) lives bundled inside acme.json. SelfPost
-# needs separate PEM files for Postfix, so an extraction step is required; see
+# Alternative reverse-proxy: Traefik. Traefik does NOT write plain PEM files —
+# everything (cert + key) lives bundled inside acme.json. SelfPost needs
+# separate PEM files for Postfix, so an extraction step is required; see
 # extract-cert.sh in this directory and the cron/systemd-timer note below.
 #
 # Merge with the base file — run this from the deploy/ directory (Compose

deploy/traefik/extract-cert.sh

@@ -1,9 +1,9 @@
 #!/bin/sh
-# Extracts a PEM cert/key pair for one domain out of Traefik's acme.json
-# (spec 10.3: "Traefik keeps certificates in acme.json, so a PEM extraction
-# step is required"). Run this on the host, after Traefik has issued or
-# renewed the certificate, and again on a schedule (cron/systemd timer) since
-# acme.json is not itself watched by SelfPost/Postfix.
+# Extracts a PEM cert/key pair for one domain out of Traefik's acme.json —
+# Traefik keeps its certificates there, so a PEM extraction step is required.
+# Run this on the host, after Traefik has issued or renewed the certificate, and
+# again on a schedule (cron/systemd timer) since acme.json is not itself watched
+# by SelfPost/Postfix.
 #
 # Requires jq. Usage: ./extract-cert.sh <acme.json path> <domain> <output dir>
 set -eu