T9/Phase 7: deploy 4-container compose + Caddy reverse proxy

- docker-compose.yml: 4 services (db, api, spa, worker), Next.js removed
- Dockerfile.api: Bun base, install, run
- Dockerfile.worker: Bun base, install, run
- Dockerfile.spa: multi-stage (Bun build -> Caddy serve), fixed lockfile + workspace stubs
- Caddyfile: serve SPA + reverse-proxy /api/* + /mcp, SPA fallback routing
- Old Node worker stopped, replaced with new Bun worker
- Old Next.js server on :3000 stopped
- BASELINE.md: Phase 7 Deploy section added
- DEPLOY.md: deploy/rollback/debug guide added

Caddyfile

@@ -1,11 +1,17 @@
 :80 {
     root * /usr/share/caddy
-    file_server
+    encode gzip
 
-    @api path /api/* /mcp*
-    reverse_proxy @api api:3000
+    route /api/* {
+        reverse_proxy api:3000
+    }
 
-    handle_errors {
-        respond 404 "Not Found"
+    route /mcp* {
+        reverse_proxy api:3000
+    }
+
+    route {
+        try_files {path} /index.html
+        file_server
     }
 }