Wire up deployment metadata: build commit, number, and server start time; v2.0.30

- Dockerfile: expose BUILD_COMMIT and BUILD_NUMBER env vars from build args
  (was COMMIT_SHA only; server was reading BUILD_COMMIT so it always fell through to null)
- CI: pass github.run_number as BUILD_NUMBER build arg
- state.js: record serverStartedAt at module load so deployedAt always shows
  when the current container instance came up, even without an env var
- admin-content.js: fall back COMMIT_SHA → BUILD_COMMIT for older images,
  use state.serverStartedAt when DEPLOYED_AT env var not set

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.0.29",
+  "version": "2.0.30",
   "type": "module",
   "scripts": {
     "dev": "vite",