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/cffi/lock.py

@@ -0,0 +1,30 @@
+import sys
+
+if sys.version_info < (3,):
+    try:
+        from thread import allocate_lock
+    except ImportError:
+        from dummy_thread import allocate_lock
+else:
+    try:
+        from _thread import allocate_lock
+    except ImportError:
+        from _dummy_thread import allocate_lock
+
+
+##import sys
+##l1 = allocate_lock
+
+##class allocate_lock(object):
+##    def __init__(self):
+##        self._real = l1()
+##    def __enter__(self):
+##        for i in range(4, 0, -1):
+##            print sys._getframe(i).f_code
+##        print
+##        return self._real.__enter__()
+##    def __exit__(self, *args):
+##        return self._real.__exit__(*args)
+##    def acquire(self, f):
+##        assert f is False
+##        return self._real.acquire(f)