feat(admin): add ephemeral staging DB, read-only posts overview, and dynamic search

- Implement ephemeral staging mode (APP_ENV=staging) to isolate test/dev DB writes in /tmp
- Add read-only posts management dashboard under /guanli/posts with live links and comment counters
- Add hot re-indexing endpoint (/guanli/reindex) to refresh Markdown without restarting server
- Replace static recommended search config with dynamic frequency-based trending searches
- Remove early scaffold mockup file (dropbox/zh.md) and clean legacy mock test queries
- Add native Makefile with dev, dev-persistent, test, lint, and docker targets
- Update test suite and documentation for development workflows

sample-content/config.yaml

@@ -30,11 +30,6 @@ social:
   - platform: email
     address: "[email protected]"
 
-search:
-  recommended:
-    - label: 'tag:k8s "container image" category:tech'
-      query: 'tag:k8s "container image" category:tech'
-
 plugins:
   google-analytics:
     enabled: true