refactor: fix ruff bugbear and silent-except findings

- B904: chain OSError/collection errors with "raise ... from e" in
  normalize.py and searcher.py so the original traceback is preserved.
- B007: rename unused loop variables to _name in dedup, dialect, layers,
  and room_detector_local.
- S110/S112: replace bare "try/except/pass" and "try/except/continue"
  with logger.debug(..., exc_info=True) in mcp_server, searcher,
  palace, palace_graph, miner, convo_miner, and fact_checker so
  background failures are observable without changing behaviour.

A module-level logger ("mempalace_mcp", matching mcp_server/searcher)
is added to the five files that didn't already have one. Configured
ruff checks (E/F/W/C901) and ruff --select B, S110, S112 all pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

mempalace/mcp_server.py

@@ -900,7 +900,7 @@ def tool_add_drawer(
         if existing and existing["ids"]:
             return {"success": True, "reason": "already_exists", "drawer_id": drawer_id}
     except Exception:
-        pass
+        logger.debug("Idempotency pre-check failed for %s", drawer_id, exc_info=True)
 
     try:
         col.upsert(
@@ -1418,7 +1418,7 @@ def tool_hook_settings(silent_save: bool = None, desktop_toast: bool = None):
     try:
         config = MempalaceConfig()
     except Exception:
-        pass
+        logger.debug("Could not re-read config after update", exc_info=True)
 
     result = {
         "success": True,