Implement image upload functionality with metadata storage; update frontend to display uploaded images

Co-authored-by: Copilot <copilot@github.com>

backend/app/db.py

@@ -64,3 +64,14 @@ def _run_migrations(conn: duckdb.DuckDBPyConnection) -> None:
             revoked     BOOLEAN   DEFAULT false
         )
     """)
+    conn.execute("""
+        CREATE TABLE IF NOT EXISTS uploaded_images (
+            id           UUID      DEFAULT uuid() PRIMARY KEY,
+            user_id      UUID      NOT NULL,
+            filename     VARCHAR   NOT NULL,
+            content_type VARCHAR   NOT NULL,
+            file_path    VARCHAR   NOT NULL,
+            size_bytes   BIGINT    NOT NULL,
+            created_at   TIMESTAMP DEFAULT now()
+        )
+    """)