Add filtering functionality to server list endpoint (#374)

## Summary
- Adds `updated_since`, `search`, and `version` query parameters to `GET
/v0/servers`
- Enables incremental synchronization via RFC3339 timestamp filtering
- Provides simple substring search on server names
- Supports latest version filtering with `version=latest`

This implementation provides the core filtering capabilities needed for
efficient registry synchronization and improved server discovery.

Fixes #291
Fixes #135

docs/reference/api/official-registry-api.md

@@ -33,6 +33,19 @@ See [Publisher Commands](../cli/commands.md) for authentication setup.
 
 The official registry enforces additional [package validation requirements](../server-json/official-registry-requirements.md) when publishing.
 
+### Server List Filtering
+
+The official registry extends the `GET /v0/servers` endpoint with additional query parameters for improved discovery and synchronization:
+
+- `updated_since` - Filter servers updated after RFC3339 timestamp (e.g., `2025-08-07T13:15:04.280Z`)
+- `search` - Case-insensitive substring search on server names (e.g., `filesystem`)  
+    - This is intentionally simple. For more advanced searching and filtering, use a subregistry.
+- `version` - Filter by version (currently supports `latest` for latest versions only)
+
+These extensions enable efficient incremental synchronization for downstream registries and improved server discovery. Parameters can be combined and work with standard cursor-based pagination.
+
+Example: `GET /v0/servers?search=filesystem&updated_since=2025-08-01T00:00:00Z&version=latest`
+
 ### Additional endpoints
 
 #### Auth endpoints