feat(migration): implement interactive mapping resolution workflow

- Add SQLite database integration for environments and mappings
- Update TaskManager to support pausing tasks (AWAITING_MAPPING)
- Modify MigrationPlugin to detect missing mappings and wait for resolution
- Add frontend UI for handling missing mappings interactively
- Create dedicated migration routes and API endpoints
- Update .gitignore and project documentation

specs/001-migration-ui-redesign/contracts/api.md

@@ -0,0 +1,115 @@
+# API Contracts: Migration Process and UI Redesign
+
+## Environment Management
+
+### GET /api/environments
+List all configured environments.
+
+**Response (200 OK)**:
+```json
+[
+  {
+    "id": "uuid",
+    "name": "Development",
+    "url": "https://superset-dev.example.com"
+  }
+]
+```
+
+### GET /api/environments/{id}/databases
+Fetch the list of databases from a specific environment.
+
+**Response (200 OK)**:
+```json
+[
+  {
+    "uuid": "db-uuid",
+    "database_name": "Dev Clickhouse",
+    "engine": "clickhouse"
+  }
+]
+```
+
+## Database Mapping
+
+### GET /api/mappings
+List all saved database mappings.
+
+**Query Parameters**:
+- `source_env_id`: Filter by source environment.
+- `target_env_id`: Filter by target environment.
+
+**Response (200 OK)**:
+```json
+[
+  {
+    "id": "uuid",
+    "source_env_id": "uuid",
+    "target_env_id": "uuid",
+    "source_db_uuid": "uuid",
+    "target_db_uuid": "uuid",
+    "source_db_name": "Dev Clickhouse",
+    "target_db_name": "Prod Clickhouse"
+  }
+]
+```
+
+### POST /api/mappings
+Create or update a database mapping.
+
+**Request Body**:
+```json
+{
+  "source_env_id": "uuid",
+  "target_env_id": "uuid",
+  "source_db_uuid": "uuid",
+  "target_db_uuid": "uuid"
+}
+```
+
+### POST /api/mappings/suggest
+Get suggested mappings based on fuzzy matching.
+
+**Request Body**:
+```json
+{
+  "source_env_id": "uuid",
+  "target_env_id": "uuid"
+}
+```
+
+**Response (200 OK)**:
+```json
+[
+  {
+    "source_db_uuid": "uuid",
+    "target_db_uuid": "uuid",
+    "confidence": 0.95
+  }
+]
+```
+
+## Migration Execution
+
+### POST /api/migrations
+Start a migration job.
+
+**Request Body**:
+```json
+{
+  "source_env_id": "uuid",
+  "target_env_id": "uuid",
+  "assets": [
+    {"type": "dashboard", "id": 123}
+  ],
+  "replace_db": true
+}
+```
+
+**Response (202 Accepted)**:
+```json
+{
+  "job_id": "uuid",
+  "status": "RUNNING"
+}
+```