feat: v9.8.1 pre-built Docker images and GHCR release workflow

Setup.py now asks whether to pull pre-built images from GHCR
(recommended) or build from source. Pre-built mode skips the
15-minute compile step entirely.

- Add .github/workflows/release.yml (builds+pushes 4 images on tag)
- Add docker-compose.build.yml (source-build overlay)
- Switch docker-compose.prod.yml from build: to image: refs
- Add --build-mode CLI arg and wizard step to setup.py
- Bump version to 9.8.1 across all files
- Document TOD_VERSION env var in CONFIGURATION.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/website/index.html

@@ -55,7 +55,7 @@
       "Zero-knowledge authentication (SRP-6a)"
     ],
     "softwareRequirements": "Docker, PostgreSQL 17, Redis, NATS",
-    "softwareVersion": "9.8.0",
+    "softwareVersion": "9.8.1",
     "license": "https://mariadb.com/bsl11/"
   }
   </script>
@@ -547,7 +547,7 @@
       <section class="wp-section">
         <h2>Status</h2>
         <table class="wp-status-table">
-          <tr><td>Version</td><td>9.8.0</td></tr>
+          <tr><td>Version</td><td>9.8.1</td></tr>
           <tr><td>License</td><td>BSL 1.1 (converts to Apache 2.0 in 2030)</td></tr>
           <tr><td>Free tier</td><td>250 devices</td></tr>
           <tr><td>Stability</td><td>Breaking changes expected before v11</td></tr>