feat: implement plugin architecture and application settings with Svelte UI

- Added plugin base and loader for backend extensibility
- Implemented application settings management with config persistence
- Created Svelte-based frontend with Dashboard and Settings pages
- Added API routes for plugins, tasks, and settings
- Updated documentation and specifications
- Improved project structure and developer tools

specs/002-app-settings/plan.md

@@ -0,0 +1,102 @@
+# Technical Plan: Web Application Settings Mechanism
+
+This plan outlines the implementation of a settings management system for the Superset Tools application, allowing users to configure multiple Superset environments and global application settings (like backup storage) via the web UI.
+
+## 1. Backend Architecture
+
+### 1.1 Data Models (Pydantic)
+
+We will define models in `backend/src/core/config_models.py`:
+
+```python
+from pydantic import BaseModel, Field
+from typing import List, Optional
+
+class Environment(BaseModel):
+    id: str
+    name: str
+    url: str
+    username: str
+    password: str  # Will be masked in UI
+    is_default: bool = False
+
+class GlobalSettings(BaseModel):
+    backup_path: str
+    default_environment_id: Optional[str] = None
+
+class AppConfig(BaseModel):
+    environments: List[Environment] = []
+    settings: GlobalSettings
+```
+
+### 1.2 Configuration Manager
+
+A new class `ConfigManager` in `backend/src/core/config_manager.py` will handle:
+- Loading/saving `AppConfig` to `config.json`.
+- CRUD operations for environments.
+- Updating global settings.
+- Validating backup paths and Superset URLs.
+
+### 1.3 API Endpoints
+
+New router `backend/src/api/routes/settings.py`:
+
+- `GET /settings`: Retrieve all settings (masking passwords).
+- `PATCH /settings/global`: Update global settings (backup path, etc.).
+- `GET /settings/environments`: List all environments.
+- `POST /settings/environments`: Add a new environment.
+- `PUT /settings/environments/{id}`: Update an environment.
+- `DELETE /settings/environments/{id}`: Remove an environment.
+- `POST /settings/environments/{id}/test`: Test connection to a specific environment.
+
+### 1.4 Integration
+
+- Update `backend/src/dependencies.py` to provide a singleton `ConfigManager`.
+- Refactor `superset_tool/utils/init_clients.py` to fetch environment details from `ConfigManager` instead of hardcoded values.
+
+## 2. Frontend Implementation
+
+### 2.1 Settings Page
+
+- Create `frontend/src/pages/Settings.svelte`.
+- Add a "Settings" link to the main navigation (likely in `App.svelte`).
+
+### 2.2 Components
+
+- **EnvironmentList**: Displays a table/list of configured environments with Edit/Delete buttons.
+- **EnvironmentForm**: A modal or inline form for adding/editing environments.
+- **GlobalSettingsForm**: Form for editing the backup storage path.
+
+### 2.3 API Integration
+
+- Add functions to `frontend/src/lib/api.js` for interacting with the new settings endpoints.
+
+## 3. Workflow Diagram
+
+```mermaid
+graph TD
+    UI[Web UI - Settings Page] --> API[FastAPI Settings Router]
+    API --> CM[Config Manager]
+    CM --> JSON[(config.json)]
+    CM --> SS[Superset Instance] : Test Connection
+    
+    Plugins[Plugins - Backup/Migration] --> CM : Get Env/Path
+```
+
+## 4. Implementation Steps
+
+1.  **Backend Core**:
+    - Create `config_models.py` and `config_manager.py`.
+    - Implement file-based persistence.
+2.  **Backend API**:
+    - Implement `settings.py` router.
+    - Register router in `app.py`.
+3.  **Frontend UI**:
+    - Create `Settings.svelte` and necessary components.
+    - Implement API calls and state management.
+4.  **Refactoring**:
+    - Update `init_clients.py` to use the new configuration system.
+    - Ensure existing plugins (Backup, Migration) use the configured settings.
+5.  **Validation**:
+    - Add path existence/write checks for backup storage.
+    - Add URL/Connection checks for Superset environments.