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/bcrypt/__init__.py

@@ -0,0 +1,43 @@
+# 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
+#
+# http://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.
+
+from ._bcrypt import (
+    __author__,
+    __copyright__,
+    __email__,
+    __license__,
+    __summary__,
+    __title__,
+    __uri__,
+    checkpw,
+    gensalt,
+    hashpw,
+    kdf,
+)
+from ._bcrypt import (
+    __version_ex__ as __version__,
+)
+
+__all__ = [
+    "__author__",
+    "__copyright__",
+    "__email__",
+    "__license__",
+    "__summary__",
+    "__title__",
+    "__uri__",
+    "__version__",
+    "checkpw",
+    "gensalt",
+    "hashpw",
+    "kdf",
+]

venv/lib/python3.12/site-packages/bcrypt/__init__.pyi

@@ -0,0 +1,10 @@
+def gensalt(rounds: int = 12, prefix: bytes = b"2b") -> bytes: ...
+def hashpw(password: bytes, salt: bytes) -> bytes: ...
+def checkpw(password: bytes, hashed_password: bytes) -> bool: ...
+def kdf(
+    password: bytes,
+    salt: bytes,
+    desired_key_bytes: int,
+    rounds: int,
+    ignore_few_rounds: bool = False,
+) -> bytes: ...