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/requests/packages.py

@@ -0,0 +1,23 @@
+import sys
+
+from .compat import chardet
+
+# This code exists for backwards compatibility reasons.
+# I don't like it either. Just look the other way. :)
+
+for package in ("urllib3", "idna"):
+    locals()[package] = __import__(package)
+    # This traversal is apparently necessary such that the identities are
+    # preserved (requests.packages.urllib3.* is urllib3.*)
+    for mod in list(sys.modules):
+        if mod == package or mod.startswith(f"{package}."):
+            sys.modules[f"requests.packages.{mod}"] = sys.modules[mod]
+
+if chardet is not None:
+    target = chardet.__name__
+    for mod in list(sys.modules):
+        if mod == target or mod.startswith(f"{target}."):
+            imported_mod = sys.modules[mod]
+            sys.modules[f"requests.packages.{mod}"] = imported_mod
+            mod = mod.replace(target, "chardet")
+            sys.modules[f"requests.packages.{mod}"] = imported_mod