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/pygments/modeline.py

@@ -0,0 +1,43 @@
+"""
+    pygments.modeline
+    ~~~~~~~~~~~~~~~~~
+
+    A simple modeline parser (based on pymodeline).
+
+    :copyright: Copyright 2006-present by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+import re
+
+__all__ = ['get_filetype_from_buffer']
+
+
+modeline_re = re.compile(r'''
+    (?: vi | vim | ex ) (?: [<=>]? \d* )? :
+    .* (?: ft | filetype | syn | syntax ) = ( [^:\s]+ )
+''', re.VERBOSE)
+
+
+def get_filetype_from_line(l): # noqa: E741
+    m = modeline_re.search(l)
+    if m:
+        return m.group(1)
+
+
+def get_filetype_from_buffer(buf, max_lines=5):
+    """
+    Scan the buffer for modelines and return filetype if one is found.
+    """
+    lines = buf.splitlines()
+    for line in lines[-1:-max_lines-1:-1]:
+        ret = get_filetype_from_line(line)
+        if ret:
+            return ret
+    for i in range(max_lines, -1, -1):
+        if i < len(lines):
+            ret = get_filetype_from_line(lines[i])
+            if ret:
+                return ret
+
+    return None