feat(doctor): add count-based database size check (#724)

feat(doctor): add count-based database size check

Adds CheckDatabaseSize (Check 29) that warns when closed issues exceed a configurable threshold (default: 5000). The check is informational only - no auto-fix since pruning is destructive.

Also improves fix guidance for sync-branch hook compatibility and legacy JSONL filename checks.

PR #724 by @rsnodgrass

cmd/bd/doctor.go

@@ -422,6 +422,10 @@ func applyFixList(path string, fixes []doctorCheck) {
 			// No auto-fix: compaction requires agent review
 			fmt.Printf("  ⚠ Run 'bd compact --analyze' to review candidates\n")
 			continue
+		case "Large Database":
+			// No auto-fix: pruning deletes data, must be user-controlled
+			fmt.Printf("  ⚠ Run 'bd cleanup --older-than 90' to prune old closed issues\n")
+			continue
 		default:
 			fmt.Printf("  ⚠ No automatic fix available for %s\n", check.Name)
 			fmt.Printf("  Manual fix: %s\n", check.Fix)
@@ -817,6 +821,12 @@ func runDiagnostics(path string) doctorResult {
 	result.Checks = append(result.Checks, compactionCheck)
 	// Info only, not a warning - compaction requires human review
 
+	// Check 29: Database size (pruning suggestion)
+	// Note: This check has no auto-fix - pruning is destructive and user-controlled
+	sizeCheck := convertDoctorCheck(doctor.CheckDatabaseSize(path))
+	result.Checks = append(result.Checks, sizeCheck)
+	// Don't fail overall check for size warning, just inform
+
 	return result
 }