fix: prevent memory overflow from excessive logging in streaming and query processing (#1879)

* Initial plan

* fix: reduce excessive logging to prevent memory overflow

- Add log file rotation (10MB max per file, 5 backups)
- Reduce streaming response logging (every 10th chunk instead of every chunk)
- Remove debug logging from controller tight loop
- Add summary logging after streaming completes

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* refactor: address code review feedback

- Extract log rotation config to module-level constants
- Keep first streaming chunk at INFO level for connection debugging
- Use DEBUG level for subsequent chunks

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

* style: fix code formatting whitespace

Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: RockChinQ <45992437+RockChinQ@users.noreply.github.com>

src/langbot/pkg/pipeline/controller.py

@@ -33,11 +33,14 @@ class Controller:
 
                     for query in queries:
                         session = await self.ap.sess_mgr.get_session(query)
-                        self.ap.logger.debug(f'Checking query {query} session {session}')
+                        # Debug logging removed from tight loop to prevent excessive log generation
+                        # that can cause memory overflow in high-traffic scenarios
 
                         if not session._semaphore.locked():
                             selected_query = query
                             await session._semaphore.acquire()
+                            # Only log when actually selecting a query
+                            self.ap.logger.debug(f'Selected query {query.query_id} for processing')
 
                             break