fix(ci): enhance rate limit integration test reliability

- Added HTTP status checks for login and security config POST requests to ensure proper error handling.
- Implemented a readiness gate for the Caddy admin API before applying security configurations.
- Increased sleep duration before verifying rate limit handler to accommodate Caddy's configuration propagation.
- Changed verification failure from a warning to a hard exit to prevent misleading test results.
- Updated Caddy admin API URL to use the canonical trailing slash in multiple locations.
- Adjusted retry parameters for rate limit verification to reduce polling noise.
- Removed stale GeoIP checksum validation from the Dockerfile's non-CI path to simplify the build process.

.github/workflows/rate-limit-integration.yml

@@ -68,7 +68,7 @@ jobs:
 
             echo "### Caddy Admin Config (rate_limit handlers)"
             echo '```json'
-            curl -s http://localhost:2119/config 2>/dev/null | grep -A 20 '"handler":"rate_limit"' | head -30 || echo "Could not retrieve Caddy config"
+            curl -s http://localhost:2119/config/ 2>/dev/null | grep -A 20 '"handler":"rate_limit"' | head -30 || echo "Could not retrieve Caddy config"
             echo '```'
             echo ""