fix(staleness): auto-import on stale DB for read-only commands (bd-9dao) (#982)

When database is stale and a read-only command runs in --no-daemon mode,
auto-import from JSONL instead of returning an error. This fixes `gt sling`
failing with 'not a valid bead' after git pull.

Root cause: `ensureDatabaseFresh` would return an error when DB was stale,
but read-only commands like `bd show` should be able to auto-import and
proceed rather than blocking the user.

Changes:
- Modify ensureDatabaseFresh to call autoImportIfNewer() when stale
- Only error if --no-auto-import flag is explicitly set
- Add comprehensive tests for all staleness scenarios

Fixes: bd-9dao

Co-authored-by: Claude <noreply@anthropic.com>

cmd/bd/staleness.go

@@ -43,7 +43,15 @@ func ensureDatabaseFresh(ctx context.Context) error {
 		return nil
 	}
 
-	// Database is stale - refuse to operate
+	// Database is stale - auto-import to refresh (bd-9dao fix)
+	// For read-only commands running in --no-daemon mode, auto-import instead of
+	// returning an error. This allows commands like `bd show` to work after git pull.
+	if !noAutoImport {
+		autoImportIfNewer()
+		return nil
+	}
+
+	// Auto-import is disabled, refuse to operate
 	return fmt.Errorf(
 		"Database out of sync with JSONL. Run 'bd sync --import-only' to fix.\n\n"+
 			"The JSONL file has been updated (e.g., after 'git pull') but the database\n"+