release: 1.9.4: Panel-redesign plan: component kit, stages, reorder (docs only)

Plan-only cut, owner-requested. The redesign goes first as 2.0.0 and
inbound-antispam-panel follows as 2.1.0 on the 2.0 baseline (migration
0002_inbound_spam_log.sql), built from the redesign's component kit so its
two screens are styled once. No product code changes.

Changed:
  - panel-redesign plan: Component kit section and stage 0 (partials with
    typed inputs in components.go, one panel.css, /server/components kit
    page, acceptance before any page is restyled); staged checklist (5/27);
    Health decided inside 2.0, queue pages left as old content in the new
    shell.
  - panel-redesign plan: Against resurrected pages - shrink-only
    legacyPages ratchet in the guard tests enforced by CI, the outline
    golden, the old-path test and a history-blob check, so an old template
    from git history cannot pass as a redesigned page.
  - roadmap: new candidate delivery-log-storage - the Delivery log box on a
    message page is empty for anything older than the last daily rotation
    because the lines are grepped from the current mail.log on each view
    and never stored.
  - development.md version table, image pin 1.9.4 in compose, README, guide.

Full detail: CHANGELOG.md (1.9.4).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -112,7 +112,7 @@ docker run --rm -d --name selfpost-try \
   -e SELFPOST_HOSTNAME=mail.local.test \
   -e PANEL_COOKIE_SECURE=false \
   -v selfpost-try-data:/data \
-  ghcr.io/mixeme/selfpost:1.9.3
+  ghcr.io/mixeme/selfpost:1.9.4
 ```
 
 **Get the setup URL** (pick one):