feat(confs): integrate dnfs service with centralized config management

- Add dnfs.ini to confs/configs/ with server, database, ai_review, confs sections
- Refactor dnfs.py to use three-layer fail-safe config loading (defaults → confs → env vars)
- Unify timeouts for DB RPC and AI review calls via configuration
- Add _merge_ini() whitelist merging to prevent unexpected config injection
- Environment variables have highest priority for Docker networking (db/ai_review hostnames)
- Document config loading mechanism in both confs/README.md and dnfs/README.md

Follows the same pattern as static service integration; confs failure falls back
gracefully to built-in defaults + environment variables.

confs/configs/dnfs.ini

@@ -0,0 +1,16 @@
+[server]
+host = 127.0.0.1
+port = 8006
+
+[database]
+host = 127.0.0.1
+port = 8005
+timeout = 10
+
+[ai_review]
+url = http://127.0.0.1:8007/review
+timeout = 10
+
+[confs]
+host = 127.0.0.1
+port = 8010