Prep v1.1.0 release: version string, gitignore secrets, docs

- Add VERSION = "1.1.0" to server.py; print at startup, expose via public
  GET /api/config, and show it in the admin header (so deployed == released
  is verifiable at a glance).
- Ignore config.json in .gitignore — it holds the admin password hash and
  session secret; fresh installs use config.json.example.
- README/CLAUDE.md: document the in-app pixel editor (now with shape tools,
  select/move, reference overlay, custom/recent palettes), the receiver health
  dashboard, 9 sprite types, and the asset cache-busting convention.
- Bump admin asset cache-bust to ?v=20260609d.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

admin/admin.css

@@ -169,6 +169,15 @@ textarea {
     margin: 0;
 }
 
+.admin-version {
+    font-family: 'Courier New', monospace;
+    font-size: 11px;
+    color: #54fc54;
+    text-shadow: none;
+    margin-left: 6px;
+    vertical-align: middle;
+}
+
 .header-actions {
     display: flex;
     gap: 8px;