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/terminalprogress.py

@@ -0,0 +1,30 @@
+# A plugin to register the TerminalProgressPlugin plugin.
+#
+# This plugin is not loaded by default due to compatibility issues (#13896),
+# but can be enabled in one of these ways:
+# - The terminal plugin enables it in a few cases where it's safe, and not
+#   blocked by the user (using e.g. `-p no:terminalprogress`).
+# - The user explicitly requests it, e.g. using `-p terminalprogress`.
+#
+# In a few years, if it's safe, we can consider enabling it by default. Then,
+# this file will become unnecessary and can be inlined into terminal.py.
+
+from __future__ import annotations
+
+import os
+
+from _pytest.config import Config
+from _pytest.config import hookimpl
+from _pytest.terminal import TerminalProgressPlugin
+from _pytest.terminal import TerminalReporter
+
+
+@hookimpl(trylast=True)
+def pytest_configure(config: Config) -> None:
+    reporter: TerminalReporter | None = config.pluginmanager.get_plugin(
+        "terminalreporter"
+    )
+
+    if reporter is not None and reporter.isatty() and os.environ.get("TERM") != "dumb":
+        plugin = TerminalProgressPlugin(reporter)
+        config.pluginmanager.register(plugin, name="terminalprogress-plugin")