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/ecdsa/_version.py

@@ -0,0 +1,21 @@
+
+# This file was generated by 'versioneer.py' (0.21) from
+# revision-control system data, or from the parent directory name of an
+# unpacked source archive. Distribution tarballs contain a pre-generated copy
+# of this file.
+
+import json
+
+version_json = '''
+{
+ "date": "2026-03-26T10:50:34+0100",
+ "dirty": false,
+ "error": null,
+ "full-revisionid": "bd66899550d7185939bf27b75713a2ac9325a9d3",
+ "version": "0.19.2"
+}
+'''  # END VERSION_JSON
+
+
+def get_versions():
+    return json.loads(version_json)