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/room_detector_local.py

@@ -202,7 +202,7 @@ def detect_rooms_from_files(project_dir: str) -> list:
 
     SKIP_DIRS = {".git", "node_modules", "__pycache__", ".venv", "venv", "dist", "build"}
 
-    for root, dirs, filenames in os.walk(project_path):
+    for _root, dirs, filenames in os.walk(project_path):
         dirs[:] = [d for d in dirs if d not in SKIP_DIRS]
         for filename in filenames:
             name_lower = filename.lower().replace("-", "_").replace(" ", "_")