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/jose/exceptions.py

@@ -0,0 +1,59 @@
+class JOSEError(Exception):
+    pass
+
+
+class JWSError(JOSEError):
+    pass
+
+
+class JWSSignatureError(JWSError):
+    pass
+
+
+class JWSAlgorithmError(JWSError):
+    pass
+
+
+class JWTError(JOSEError):
+    pass
+
+
+class JWTClaimsError(JWTError):
+    pass
+
+
+class ExpiredSignatureError(JWTError):
+    pass
+
+
+class JWKError(JOSEError):
+    pass
+
+
+class JWEError(JOSEError):
+    """Base error for all JWE errors"""
+
+    pass
+
+
+class JWEParseError(JWEError):
+    """Could not parse the JWE string provided"""
+
+    pass
+
+
+class JWEInvalidAuth(JWEError):
+    """
+    The authentication tag did not match the protected sections of the
+    JWE string provided
+    """
+
+    pass
+
+
+class JWEAlgorithmUnsupportedError(JWEError):
+    """
+    The JWE algorithm is not supported by the backend
+    """
+
+    pass