refactor: streamline ALLOWED_ROOT_DIRECTORY handling and remove legacy support

This commit refactors the handling of ALLOWED_ROOT_DIRECTORY by removing legacy support for ALLOWED_PROJECT_DIRS and simplifying the security logic. Key changes include:

- Removed deprecated ALLOWED_PROJECT_DIRS references from .env.example and security.ts.
- Updated initAllowedPaths() to focus solely on ALLOWED_ROOT_DIRECTORY and DATA_DIR.
- Enhanced logging for ALLOWED_ROOT_DIRECTORY configuration status.
- Adjusted route handlers to utilize the new workspace directory logic.
- Introduced a centralized storage module for localStorage operations to improve consistency and error handling.

These changes aim to enhance security and maintainability by consolidating directory management into a single variable.

Tests: All unit tests passing.

apps/ui/src/lib/http-api-client.ts

@@ -766,6 +766,7 @@ export class HttpApiClient implements ElectronAPI {
       success: boolean;
       configured: boolean;
       workspaceDir?: string;
+      defaultDir?: string | null;
       error?: string;
     }> => this.get("/api/workspace/config"),