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/request.pyx

@@ -0,0 +1,65 @@
+cdef class UVRequest:
+    """A base class for all libuv requests (uv_getaddrinfo_t, etc).
+
+    Important: it's a responsibility of the subclass to call the
+    "on_done" method in the request's callback.
+
+    If "on_done" isn't called, the request object will never die.
+    """
+
+    def __cinit__(self, Loop loop, *_):
+        self.request = NULL
+        self.loop = loop
+        self.done = 0
+        Py_INCREF(self)
+
+    cdef on_done(self):
+        self.done = 1
+        Py_DECREF(self)
+
+    cdef cancel(self):
+        # Most requests are implemented using a threadpool.  It's only
+        # possible to cancel a request when it's still in a threadpool's
+        # queue.  Once it's started to execute, we have to wait until
+        # it finishes and calls its callback (and callback *must* call
+        # UVRequest.on_done).
+
+        cdef int err
+
+        if self.done == 1:
+            return
+
+        if UVLOOP_DEBUG:
+            if self.request is NULL:
+                raise RuntimeError(
+                    '{}.cancel: .request is NULL'.format(
+                        self.__class__.__name__))
+
+            if self.request.data is NULL:
+                raise RuntimeError(
+                    '{}.cancel: .request.data is NULL'.format(
+                        self.__class__.__name__))
+
+            if <UVRequest>self.request.data is not self:
+                raise RuntimeError(
+                    '{}.cancel: .request.data is not UVRequest'.format(
+                        self.__class__.__name__))
+
+        # We only can cancel pending requests.  Let's try.
+        err = uv.uv_cancel(self.request)
+        if err < 0:
+            if err == uv.UV_EBUSY:
+                # Can't close the request -- it's executing (see the first
+                # comment).  Loop will have to wait until the callback
+                # fires.
+                pass
+            elif err == uv.UV_EINVAL:
+                # From libuv docs:
+                #
+                #     Only cancellation of uv_fs_t, uv_getaddrinfo_t,
+                #     uv_getnameinfo_t and uv_work_t requests is currently
+                #     supported.
+                return
+            else:
+                ex = convert_error(err)
+                self.loop._handle_exception(ex)