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/stream.pxd

@@ -0,0 +1,50 @@
+cdef class UVStream(UVBaseTransport):
+    cdef:
+        uv.uv_shutdown_t _shutdown_req
+        bint __shutting_down
+        bint __reading
+        bint __read_error_close
+
+        bint __buffered
+        object _protocol_get_buffer
+        object _protocol_buffer_updated
+
+        bint _eof
+        list _buffer
+        size_t _buffer_size
+
+        Py_buffer _read_pybuf
+        bint _read_pybuf_acquired
+
+    # All "inline" methods are final
+
+    cdef inline _init(self, Loop loop, object protocol, Server server,
+                      object waiter, object context)
+
+
+    cdef inline _shutdown(self)
+    cdef inline _accept(self, UVStream server)
+
+    cdef inline _close_on_read_error(self)
+
+    cdef inline __reading_started(self)
+    cdef inline __reading_stopped(self)
+
+    # The user API write() and writelines() firstly call _buffer_write() to
+    # buffer up user data chunks, potentially multiple times in writelines(),
+    # and then call _initiate_write() to start writing either immediately or in
+    # the next iteration (loop._queue_write()).
+    cdef inline _buffer_write(self, object data)
+    cdef inline _initiate_write(self)
+
+    # _exec_write() is the method that does the actual send, and _try_write()
+    # is a fast-path used in _exec_write() to send a single chunk.
+    cdef inline _exec_write(self)
+    cdef inline _try_write(self, object data)
+
+    cdef _close(self)
+
+    cdef inline _on_accept(self)
+    cdef inline _on_eof(self)
+    cdef inline _on_write(self)
+    cdef inline _on_connect(self, object exc)