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/cbhandles.pxd

@@ -0,0 +1,39 @@
+cdef class Handle:
+    cdef:
+        Loop loop
+        object context
+        bint _cancelled
+
+        str meth_name
+        int cb_type
+        void *callback
+        object arg1, arg2, arg3, arg4
+
+        object __weakref__
+
+        readonly _source_traceback
+
+    cdef inline _set_loop(self, Loop loop)
+    cdef inline _set_context(self, object context)
+
+    cdef inline _run(self)
+    cdef _cancel(self)
+
+    cdef _format_handle(self)
+
+
+cdef class TimerHandle:
+    cdef:
+        object callback
+        tuple args
+        bint _cancelled
+        UVTimer timer
+        Loop loop
+        object context
+        tuple _debug_info
+        object __weakref__
+        object _when
+
+    cdef _run(self)
+    cdef _cancel(self)
+    cdef inline _clear(self)