feat: ✨ implement geo-filtering with whitelist and blacklist support

- Added support for geo-filtering in the proxy pool, allowing configuration of allowed and blocked countries via environment variables.
- Updated `.env.example` and `docker-compose.yml` to include `ALLOWED_COUNTRIES` for whitelist functionality.
- Enhanced `CLAUDE.md`, `GEO_FILTER.md`, and `README.md` to document the new geo-filtering features and usage instructions.
- Modified proxy validation logic to prioritize whitelist over blacklist during admission checks.
- Improved WebUI to allow dynamic configuration of geo-filter settings.

docker-compose.yml

@@ -25,6 +25,7 @@ services:
       - PROXY_AUTH_USERNAME=${PROXY_AUTH_USERNAME:-proxy}
       - PROXY_AUTH_PASSWORD=${PROXY_AUTH_PASSWORD}
       - BLOCKED_COUNTRIES=${BLOCKED_COUNTRIES:-CN}
+      - ALLOWED_COUNTRIES=${ALLOWED_COUNTRIES}
     healthcheck:
       test: ["CMD", "wget", "-qO-", "http://localhost:7778/"]
       interval: 30s