fix(docker): move the app and bot images to Node 22.23.4 (Node2Shell)

CVE-2026-111497 ("Node2Shell") is an out-of-bounds write in the Brotli
decoder Node bundles; it was fixed on 2026-10-21 in 22.23.4, 24.22.1 and
26.12.1. Both images were on node:20-alpine, and Node 20 is past end of
life, so it gets no fix.

The site is not reachable through the main path (Express 4 / body-parser
1.20 refuse a `br` request body with 415, and nothing calls the zlib
Brotli API), but fetch() decodes Brotli responses and the runtime itself
was unpatched. Pin the exact patched version so a floating tag cannot
hold an old build, and run CI on the same version the image ships.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

README.md

@@ -147,7 +147,7 @@ flowchart TB
 
 | Layer | Tech |
 |---|---|
-| Backend | Node.js 20+, Express 4, `mariadb` driver (parameterized SQL, no ORM) |
+| Backend | Node.js 22 (images pin 22.23.4), Express 4, `mariadb` driver (parameterized SQL, no ORM) |
 | Auth | Session service over JWT: httpOnly cookie (web) + bearer access/refresh tokens (mobile), bcrypt hashing, optional TOTP 2FA (`speakeasy` + `qrcode`), pluggable OAuth2/OIDC SSO (built-in Google & Discord + generic) |
 | Database | MariaDB 11 (own container) |
 | Frontend | React 18, Vite 5, React Router 6 |
@@ -196,7 +196,8 @@ website/
 
 ## Prerequisites
 
-- **Node.js 20+** and npm (Node 22/24 are fine).
+- **Node.js 22.23.4+** (or 24.22.1+) and npm. Older builds carry the Node2Shell Brotli bug
+  (CVE-2026-111497), and Node 20 is past end of life.
 - **Docker Desktop** (for MariaDB, and for the full Compose deploy).
 
 ---