feat(memory): add force_boundary flag to API to fix bulk import queue stalls

[GoodDaySolution]

Problem

Third-party clients bulk-importing historical conversation chunks (e.g. Chrome extensions importing scraped chats) frequently observe their messages getting permanently stuck in the sync_status = -1 queue. Because these imports are one-time events, the [ConvMemCellExtractor]'s LLM-based time-gap detection never triggers should_end = True, causing silent failures (empty groups).

Solution

This PR introduces a force_boundary boolean flag to the API layer, allowing clients to explicitly signal that an imported batch is complete and should bypass the LLM should_wait logic.

Changes Included:

1. [src/api_specs/dtos/memory.py]: Added force_boundary: bool = False to [MemorizeMessageRequest] and [MemorizeRequest] DTOs.
2. [src/api_specs/request_converter.py]: Updated [convert_simple_message_to_memorize_request] to extract the flag from the JSON payload.
3. [src/memory_layer/memory_manager.py] & [src/biz_layer/mem_memorize.py]: Threaded the force_boundary parameter down into the MemCell ExtractRequest abstractions.
4. [src/memory_layer/memcell_extractor/conv_memcell_extractor.py]: Modified [extract_memcell] to intercept the flag:

   if getattr(request, 'force_boundary', False):
       boundary_detection_result = BoundaryDetectionResult(
           should_end=True,
           should_wait=False,
           reasoning="Force boundary requested by client API payload",
           confidence=1.0,
           topic_summary="",
       )
   else:
       # ... fallback to standard LLM detection

How to Test

1. Send a batch of 5 short messages (under the 50 msg limit) to /api/v0/memories.
2. On the 5th message payload, attach "force_boundary": true.
3. Verify that the system immediately writes the MemCell to the database, skipping the accumulation wait period.

Note to Maintainers: I have also noted an issue where /api/v1/ routing fails on the live Cloud Gateway, and strict but silent whitelisting on the source field. Please review if those configurations on the API Gateway are intended.