fix(dolt): add hook compatibility check and migration warning

Two improvements for Dolt backend users with stale git hooks:

1. Migration warning: When running 'bd migrate --to-dolt', warn if
   installed hooks lack the Dolt backend check and suggest reinstalling.

2. Doctor check: New CheckGitHooksDoltCompatibility() detects when
   hooks exist but lack the Dolt skip logic, surfacing the error with
   a clear fix message.

Both changes help users who migrated to Dolt but have pre-migration
hooks that try to run JSONL sync (which fails with Dolt backend).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmd/bd/doctor.go

@@ -281,6 +281,13 @@ func runDiagnostics(path string) doctorResult {
 		result.OverallOK = false
 	}
 
+	// Check git hooks Dolt compatibility (hooks without Dolt check cause errors)
+	doltHooksCheck := convertWithCategory(doctor.CheckGitHooksDoltCompatibility(path), doctor.CategoryGit)
+	result.Checks = append(result.Checks, doltHooksCheck)
+	if doltHooksCheck.Status == statusError {
+		result.OverallOK = false
+	}
+
 	// If no .beads/, skip remaining checks
 	if installCheck.Status != statusOK {
 		return result