feat(phase1): add image storage utilities

- Create backend/services/image_storage.py with 4 core functions:
  - sanitize_filename(): remove unsafe chars, limit to 255 chars, convert to lowercase
  - get_unique_filename(): handle collisions with UUID suffix (format: {name}_{uuid8}_{variant}.jpg)
  - ensure_image_directories(): create /images/ root and category subdirs on startup
  - save_image(): save bytes to /images/{category}/{filename}, returns relative path
- Create comprehensive test suite (22 tests) covering all functionality
- Integrate ensure_image_directories() into FastAPI startup event
- Directory structure: /images/{category}/{filename}
- Collision handling: auto-suffix with UUID if filename exists
- All tests passing, pathlib.Path for safe operations

venv/lib/python3.12/site-packages/uvloop/handles/handle.pxd

@@ -0,0 +1,48 @@
+cdef class UVHandle:
+    cdef:
+        uv.uv_handle_t *_handle
+        Loop _loop
+        readonly _source_traceback
+        bint _closed
+        bint _inited
+        object context
+
+        # Added to enable current UDPTransport implementation,
+        # which doesn't use libuv handles.
+        bint _has_handle
+
+    # All "inline" methods are final
+
+    cdef inline _start_init(self, Loop loop)
+    cdef inline _abort_init(self)
+    cdef inline _finish_init(self)
+
+    cdef inline bint _is_alive(self)
+    cdef inline _ensure_alive(self)
+
+    cdef _error(self, exc, throw)
+    cdef _fatal_error(self, exc, throw, reason=?)
+
+    cdef _warn_unclosed(self)
+
+    cdef _free(self)
+    cdef _close(self)
+
+
+cdef class UVSocketHandle(UVHandle):
+    cdef:
+        # Points to a Python file-object that should be closed
+        # when the transport is closing.  Used by pipes.  This
+        # should probably be refactored somehow.
+        object _fileobj
+        object __cached_socket
+
+    # All "inline" methods are final
+
+    cdef _fileno(self)
+
+    cdef _new_socket(self)
+    cdef inline _get_socket(self)
+    cdef inline _attach_fileobj(self, object file)
+
+    cdef _open(self, int sockfd)