fix: reduce excessive log volume by demoting per-request noise to DEBUG (#613)

Demote high-frequency per-request/per-item logs from INFO to DEBUG:
- 🔇 Client routing decisions (async_client.py) — logged every MCP tool call
- 🔇 DB migration checks (db.py) — logged every ASGI client creation
- 🔇 Vector table ensure/ready (sqlite + postgres search repos) — logged every search
- 🔇 Per-entity search index start/complete (search_service.py) — logged every file sync
- 🔇 Incremental scan details + per-file permalink updates (sync_service.py)
- 🔇 MCP search tool params and no-results (search.py)
- 📉 Log retention: "10 days" → 5 files (~50MB cap)

API v2 request/response logs remain at INFO for observability.

Closes #613

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: phernandez <paul@basicmachines.co>

src/basic_memory/api/v2/routers/knowledge_router.py

@@ -130,7 +130,7 @@ async def resolve_identifier(
         resolution_method=resolution_method,
     )
 
-    logger.info(
+    logger.debug(
         f"API v2 response: resolved '{data.identifier}' to external_id={result.external_id} via {resolution_method}"
     )