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/_pytest/setupplan.py

@@ -0,0 +1,39 @@
+from __future__ import annotations
+
+from _pytest.config import Config
+from _pytest.config import ExitCode
+from _pytest.config.argparsing import Parser
+from _pytest.fixtures import FixtureDef
+from _pytest.fixtures import SubRequest
+import pytest
+
+
+def pytest_addoption(parser: Parser) -> None:
+    group = parser.getgroup("debugconfig")
+    group.addoption(
+        "--setupplan",
+        "--setup-plan",
+        action="store_true",
+        help="Show what fixtures and tests would be executed but "
+        "don't execute anything",
+    )
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_fixture_setup(
+    fixturedef: FixtureDef[object], request: SubRequest
+) -> object | None:
+    # Will return a dummy fixture if the setuponly option is provided.
+    if request.config.option.setupplan:
+        my_cache_key = fixturedef.cache_key(request)
+        fixturedef.cached_result = (None, my_cache_key, None)
+        return fixturedef.cached_result
+    return None
+
+
+@pytest.hookimpl(tryfirst=True)
+def pytest_cmdline_main(config: Config) -> int | ExitCode | None:
+    if config.option.setupplan:
+        config.option.setuponly = True
+        config.option.setupshow = True
+    return None