Add cbm_store_check_integrity() that validates:
- projects table has <= 5 rows (1 project per .db file)
- root_path starts with / or drive letter (not numeric garbage)
Wire into resolve_store (MCP queries) and pipeline routing:
- MCP: corrupt DB auto-deleted with ERROR log, returns "not indexed"
- Pipeline: corrupt DB deleted, falls through to full reindex
Root cause: user-reported corrupt DBs had 48K rows in projects table
with node IDs in text columns. Exact write path TBD, but detection
+ auto-clean prevents the symptom from persisting.
5 unit tests: clean DB, empty DB, bad path, too many rows, NULL.