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

backend/src/core/superset_client.py

@@ -0,0 +1,57 @@
+# [DEF:backend.src.core.superset_client:Module]
+#
+# @SEMANTICS: superset, api, client, database, metadata
+# @PURPOSE:   Extends the base SupersetClient with database-specific metadata fetching.
+# @LAYER:     Core
+# @RELATION:  INHERITS_FROM -> superset_tool.client.SupersetClient
+#
+# @INVARIANT: All database metadata requests must include UUID and name.
+
+# [SECTION: IMPORTS]
+from typing import List, Dict, Optional, Tuple
+from superset_tool.client import SupersetClient as BaseSupersetClient
+from superset_tool.models import SupersetConfig
+# [/SECTION]
+
+# [DEF:SupersetClient:Class]
+# @PURPOSE: Extended SupersetClient for migration-specific operations.
+class SupersetClient(BaseSupersetClient):
+    
+    # [DEF:SupersetClient.get_databases_summary:Function]
+    # @PURPOSE: Fetch a summary of databases including uuid, name, and engine.
+    # @POST:    Returns a list of database dictionaries with 'engine' field.
+    # @RETURN:  List[Dict] - Summary of databases.
+    def get_databases_summary(self) -> List[Dict]:
+        """
+        Fetch a summary of databases including uuid, name, and engine.
+        """
+        query = {
+            "columns": ["uuid", "database_name", "backend"]
+        }
+        _, databases = self.get_databases(query=query)
+        
+        # Map 'backend' to 'engine' for consistency with contracts
+        for db in databases:
+            db['engine'] = db.pop('backend', None)
+            
+        return databases
+    # [/DEF:SupersetClient.get_databases_summary]
+
+    # [DEF:SupersetClient.get_database_by_uuid:Function]
+    # @PURPOSE: Find a database by its UUID.
+    # @PARAM:   db_uuid (str) - The UUID of the database.
+    # @RETURN:  Optional[Dict] - Database info if found, else None.
+    def get_database_by_uuid(self, db_uuid: str) -> Optional[Dict]:
+        """
+        Find a database by its UUID.
+        """
+        query = {
+            "filters": [{"col": "uuid", "op": "eq", "value": db_uuid}]
+        }
+        _, databases = self.get_databases(query=query)
+        return databases[0] if databases else None
+    # [/DEF:SupersetClient.get_database_by_uuid]
+
+# [/DEF:SupersetClient]
+
+# [/DEF:backend.src.core.superset_client]