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/data-model.md

@@ -0,0 +1,48 @@
+# Data Model: Migration Process and UI Redesign
+
+## Entities
+
+### Environment
+Represents a Superset instance.
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `id` | UUID | Primary Key |
+| `name` | String | Display name (e.g., "Development", "Production") |
+| `url` | String | Base URL of the Superset instance |
+| `credentials_id` | String | Reference to encrypted credentials in the config manager |
+
+### DatabaseMapping
+Represents a mapping between a database in the source environment and a database in the target environment.
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `id` | UUID | Primary Key |
+| `source_env_id` | UUID | Foreign Key to Environment (Source) |
+| `target_env_id` | UUID | Foreign Key to Environment (Target) |
+| `source_db_uuid` | String | UUID of the database in the source environment |
+| `target_db_uuid` | String | UUID of the database in the target environment |
+| `source_db_name` | String | Name of the database in the source environment (for UI) |
+| `target_db_name` | String | Name of the database in the target environment (for UI) |
+| `engine` | String | Database engine type (e.g., "clickhouse", "postgres") |
+
+### MigrationJob
+Represents a single migration execution.
+
+| Field | Type | Description |
+|-------|------|-------------|
+| `id` | UUID | Primary Key |
+| `source_env_id` | UUID | Foreign Key to Environment |
+| `target_env_id` | UUID | Foreign Key to Environment |
+| `status` | Enum | `PENDING`, `RUNNING`, `COMPLETED`, `FAILED`, `AWAITING_MAPPING` |
+| `replace_db` | Boolean | Whether to apply database mappings |
+| `created_at` | DateTime | Timestamp of creation |
+
+## Relationships
+- `DatabaseMapping` belongs to a pair of `Environments`.
+- `MigrationJob` references two `Environments`.
+
+## Validation Rules
+- `source_env_id` and `target_env_id` must be different.
+- `source_db_uuid` and `target_db_uuid` must belong to databases with compatible engines (optional warning).
+- Mappings must be unique for a given `(source_env_id, target_env_id, source_db_uuid)` triplet.