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/timer.pyx

@@ -0,0 +1,89 @@
+@cython.no_gc_clear
+cdef class UVTimer(UVHandle):
+    cdef _init(self, Loop loop, method_t callback, object ctx,
+               uint64_t timeout):
+
+        cdef int err
+
+        self._start_init(loop)
+
+        self._handle = <uv.uv_handle_t*> PyMem_RawMalloc(sizeof(uv.uv_timer_t))
+        if self._handle is NULL:
+            self._abort_init()
+            raise MemoryError()
+
+        err = uv.uv_timer_init(self._loop.uvloop, <uv.uv_timer_t*>self._handle)
+        if err < 0:
+            self._abort_init()
+            raise convert_error(err)
+
+        self._finish_init()
+
+        self.callback = callback
+        self.ctx = ctx
+        self.running = 0
+        self.timeout = timeout
+        self.start_t = 0
+
+    cdef stop(self):
+        cdef int err
+
+        if not self._is_alive():
+            self.running = 0
+            return
+
+        if self.running == 1:
+            err = uv.uv_timer_stop(<uv.uv_timer_t*>self._handle)
+            self.running = 0
+            if err < 0:
+                exc = convert_error(err)
+                self._fatal_error(exc, True)
+                return
+
+    cdef start(self):
+        cdef int err
+
+        self._ensure_alive()
+
+        if self.running == 0:
+            # Update libuv internal time.
+            uv.uv_update_time(self._loop.uvloop)  # void
+            self.start_t = uv.uv_now(self._loop.uvloop)
+
+            err = uv.uv_timer_start(<uv.uv_timer_t*>self._handle,
+                                    __uvtimer_callback,
+                                    self.timeout, 0)
+            if err < 0:
+                exc = convert_error(err)
+                self._fatal_error(exc, True)
+                return
+            self.running = 1
+
+    cdef get_when(self):
+        return self.start_t + self.timeout
+
+    @staticmethod
+    cdef UVTimer new(Loop loop, method_t callback, object ctx,
+                     uint64_t timeout):
+
+        cdef UVTimer handle
+        handle = UVTimer.__new__(UVTimer)
+        handle._init(loop, callback, ctx, timeout)
+        return handle
+
+
+cdef void __uvtimer_callback(
+    uv.uv_timer_t* handle,
+) noexcept with gil:
+    if __ensure_handle_data(<uv.uv_handle_t*>handle, "UVTimer callback") == 0:
+        return
+
+    cdef:
+        UVTimer timer = <UVTimer> handle.data
+        method_t cb = timer.callback
+
+    timer.running = 0
+    try:
+        cb(timer.ctx)
+    except BaseException as ex:
+        timer._error(ex, False)