Version cut 1.9.3: close the panel-redesign docs prep, bump the pin

CHANGELOG.md audited against the full commit history from the repo's
first commit (8ad56ed) through HEAD: version/date headings, entry
completeness, and technical claims against their diffs all check out,
no discrepancies found.

The Unreleased section (panel-redesign mockups, contract, and
decisions; preflight plan) is docs-only prep — development.md's own
rule would hold the cut until a product stage ships — but the owner
asked for a version cut now, so it becomes 1.9.3 (PATCH) and a fresh
Unreleased opens. Pin bumped in deploy/docker-compose.yml, README's
quickstart, guide.md, and development.md's planned-cuts table, which
also gains the new row (renumbering inbound-antispam-panel to 11).

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

docs/development.md

@@ -107,7 +107,7 @@ than the default «meaningful step» rule in [§ Commits and release build](#com
 2. Git tag `vX.Y.Z` and publish the GitHub Release only on explicit request (see
    [§ Release image](#release-image)).
 
-**Planned version cuts** (from pin `1.9.2`; adjust if semver changes mid-track):
+**Planned version cuts** (from pin `1.9.3`; adjust if semver changes mid-track):
 
 | Stage | ID | Cut |
 |---|---|---|
@@ -120,7 +120,8 @@ than the default «meaningful step» rule in [§ Commits and release build](#com
 | 7 | application auth IPs | `1.9.0` |
 | 8 | port-25 Postfix startup fix | `1.9.1` (PATCH) |
 | 9 | 2026-08-19 code review pass | `1.9.2` (PATCH) |
-| 10 | inbound-antispam-panel | `1.10.0` (planned) |
+| 10 | panel-redesign prep (docs only, owner-requested cut) | `1.9.3` (PATCH) |
+| 11 | inbound-antispam-panel | `1.10.0` (planned) |
 
 Docs-only prep (checklists in plans, no product code) uses the same per-step
 commit rule but **no** version cut until the next product stage ships.