docs: clear shipped plans and closed work out of the documents

Owner, 2026-10-18: "Надо почистить документы от устаревшего и сделанного."

- Deleted, shipped: plans/delivery-log-storage, from-header-binding,
  inbound-antispam-panel, inbound-upstream-result, panel-dkim-signing,
  panel-notifications, and the own-mta-builds analysis (its three rows
  shipped as 2.6.1, 2.7.0, 2.8.0). What outlived them moved first: when a
  filter-list counter is worth a migration, and the notifications' "when"
  table, into architecture.md; the sender check's own-process trigger into
  security.md. Code comments that cited them point at architecture.md or
  security.md; CHANGELOG keeps their names, unlinked.
- Kept, marked closed: audit-2026-10-12, assumptions-2026-10-14 and
  security-audit-2026-10-17 - the code cites their finding ids in 50-84
  files. Their file:line refs are of the tree each audited.
- roadmap.md: open work only - stage H of the security audit (the owner's),
  go-milter-upstream (the owner posts), and queue-table, which the
  redesign left undecided and only its own shipped section still named;
  Dropped and Ideas as they were. 2.x versioning instead of 1.x.
- development.md: the 47-row planned-version-cuts table (history, in the
  CHANGELOG) gone; a stage's last step now removes its roadmap item and
  plan. Docs map lists the closed audits.
- panel-redesign.md: the done checklist out; Room for roadmap items says
  which drawn screens are unbuilt and why.
- Stale facts fixed: schema-migrations.md and architecture.md at schema 14
  (0013's users columns and user_links, 0014's secure TLS mode);
  security.md's accepted risk "profile saved without the password" - the
  e-mail asks for it since 2.14.0.

Tests: go build, go vet; go test of cmd and the touched internal packages
pass except logtail's three Windows-bound rotation tests (rename of an open
file; CI is Linux). Only comments changed in Go.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/handlers/handlers_notifications_test.go

@@ -13,7 +13,7 @@ import (
 	"github.com/mixeme/selfpost/internal/web/auth"
 )
 
-// The panel pages of notifications (plans/panel-notifications.md): the user's
+// The panel pages of notifications (docs/architecture.md § Notifications): the user's
 // checkbox on Account, the instance's switch and the DNS records of the server's
 // own name on Server › Settings, and the state of those records on Server ›
 // Health. What is sent and when is internal/notify's and tested there.