feat(v4.1.0): Data Sources & Linked Databases

- Add collection_data_sources table for multi-source collections
- API: GET/POST/DELETE /db/{id}/sources/api — data source management
- API: POST /db/{id}/linked/api — create linked database (copies views/properties)
- API: POST /db/{id}/toggle-inline/api — toggle full-page vs inline
- API: POST /db/inline/api — create inline database
- Linked DB inherits workspace_id (permissions) from source
- Migration: add workspace_id + created_by to collections table
- 10 new tests (153 total)

app/db.py

@@ -462,6 +462,31 @@ def init_db():
         """)
         conn.commit()
 
+        # v4.1.0: Data Sources & Linked Databases
+        conn.execute("""
+            CREATE TABLE IF NOT EXISTS collection_data_sources (
+                id INTEGER PRIMARY KEY AUTOINCREMENT,
+                collection_id INTEGER NOT NULL REFERENCES collections(id) ON DELETE CASCADE,
+                source_collection_id INTEGER NOT NULL REFERENCES collections(id),
+                source_name TEXT DEFAULT '',
+                is_linked BOOLEAN NOT NULL DEFAULT 0,
+                position INTEGER NOT NULL DEFAULT 0,
+                created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
+                UNIQUE(collection_id, source_collection_id)
+            )
+        """)
+        # Add workspace_id to collections if missing (v4.1.0 migration)
+        try:
+            conn.execute("ALTER TABLE collections ADD COLUMN workspace_id INTEGER REFERENCES workspaces(id)")
+        except sqlite3.OperationalError:
+            pass
+        # Add created_by to collections if missing
+        try:
+            conn.execute("ALTER TABLE collections ADD COLUMN created_by INTEGER REFERENCES users(id)")
+        except sqlite3.OperationalError:
+            pass
+        conn.commit()
+
 
 @contextmanager
 def get_conn():