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/passlib/utils/md4.py

@@ -0,0 +1,29 @@
+"""
+passlib.utils.md4 - DEPRECATED MODULE, WILL BE REMOVED IN 2.0
+
+MD4 should now be looked up through ``passlib.crypto.digest.lookup_hash("md4").const``,
+which provides unified handling stdlib implementation (if present).
+"""
+#=============================================================================
+# issue deprecation warning for module
+#=============================================================================
+from warnings import warn
+warn("the module 'passlib.utils.md4' is deprecated as of Passlib 1.7, "
+     "and will be removed in Passlib 2.0, please use "
+     "'lookup_hash(\"md4\").const()' from 'passlib.crypto' instead",
+     DeprecationWarning)
+
+#=============================================================================
+# backwards compat exports
+#=============================================================================
+__all__ = ["md4"]
+
+# this should use hashlib version if available,
+# and fall back to builtin version.
+from passlib.crypto.digest import lookup_hash
+md4 = lookup_hash("md4").const
+del lookup_hash
+
+#=============================================================================
+# eof
+#=============================================================================