feat(doctor): add database corruption recovery to --fix

Adds automatic database recovery when bd doctor --fix detects corruption:
- Detects SQLite corruption (malformed database, SQLITE_CORRUPT errors)
- Backs up corrupted database before recovery attempt
- Rebuilds from JSONL if available (issues.jsonl, deletions.jsonl)
- Falls back to fresh database if JSONL unavailable
- Reports recovery results (issues imported, success/failure)

Recovery is triggered automatically by --fix when corruption is detected.
No manual intervention required.

cmd/bd/doctor/legacy.go

@@ -190,7 +190,7 @@ func CheckLegacyJSONLFilename(repoPath string) DoctorCheck {
 		Detail:  "Having multiple JSONL files can cause sync and merge conflicts.\n" +
 			"  Only one JSONL file should be used per repository.",
 		Fix: "Determine which file is current and remove the others:\n" +
-			"  1. Check 'bd stats' to see which file is being used\n" +
+			"  1. Check .beads/metadata.json for 'jsonl_export' setting\n" +
 			"  2. Verify with 'git log .beads/*.jsonl' to see commit history\n" +
 			"  3. Remove the unused file(s): git rm .beads/<unused>.jsonl\n" +
 			"  4. Commit the change",