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/multipart/__init__.py

@@ -0,0 +1,38 @@
+# Copyright 2012, Andrew Dunham
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This only works if using a file system, other loaders not implemented.
+
+import importlib.util
+import sys
+import warnings
+from pathlib import Path
+
+for p in sys.path:
+    file_path = Path(p, "multipart.py")
+    try:
+        if file_path.is_file():
+            spec = importlib.util.spec_from_file_location("multipart", file_path)
+            assert spec is not None, f"{file_path} found but not loadable!"
+            module = importlib.util.module_from_spec(spec)
+            sys.modules["multipart"] = module
+            assert spec.loader is not None, f"{file_path} must be loadable!"
+            spec.loader.exec_module(module)
+            break
+    except PermissionError:
+        pass
+else:
+    warnings.warn("Please use `import python_multipart` instead.", PendingDeprecationWarning, stacklevel=2)
+    from python_multipart import *
+    from python_multipart import __all__, __version__

venv/lib/python3.12/site-packages/multipart/decoders.py

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+from python_multipart.decoders import *

venv/lib/python3.12/site-packages/multipart/exceptions.py

@@ -0,0 +1 @@
+from python_multipart.exceptions import *

venv/lib/python3.12/site-packages/multipart/multipart.py

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+from python_multipart.multipart import *