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/httptools/parser/protocol.py

@@ -0,0 +1,15 @@
+from typing import Protocol
+
+
+class HTTPProtocol(Protocol):
+    """Used for providing static type-checking when parsing through the http protocol"""
+
+    def on_message_begin() -> None: ...
+    def on_url(url: bytes) -> None: ...
+    def on_header(name: bytes, value: bytes) -> None: ...
+    def on_headers_complete() -> None: ...
+    def on_body(body: bytes) -> None: ...
+    def on_message_complete() -> None: ...
+    def on_chunk_header() -> None: ...
+    def on_chunk_complete() -> None: ...
+    def on_status(status: bytes) -> None: ...