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/styles/autumn.py

@@ -0,0 +1,67 @@
+"""
+    pygments.styles.autumn
+    ~~~~~~~~~~~~~~~~~~~~~~
+
+    A colorful style, inspired by the terminal highlighting style.
+
+    :copyright: Copyright 2006-present by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+
+from pygments.style import Style
+from pygments.token import Keyword, Name, Comment, String, Error, \
+     Number, Operator, Generic, Whitespace
+
+
+__all__ = ['AutumnStyle']
+
+
+class AutumnStyle(Style):
+    """
+    A colorful style, inspired by the terminal highlighting style.
+    """
+    name = 'autumn'
+
+    styles = {
+        Whitespace:                 '#bbbbbb',
+
+        Comment:                    'italic #aaaaaa',
+        Comment.Preproc:            'noitalic #4c8317',
+        Comment.Special:            'italic #0000aa',
+
+        Keyword:                    '#0000aa',
+        Keyword.Type:               '#00aaaa',
+
+        Operator.Word:              '#0000aa',
+
+        Name.Builtin:               '#00aaaa',
+        Name.Function:              '#00aa00',
+        Name.Class:                 'underline #00aa00',
+        Name.Namespace:             'underline #00aaaa',
+        Name.Variable:              '#aa0000',
+        Name.Constant:              '#aa0000',
+        Name.Entity:                'bold #800',
+        Name.Attribute:             '#1e90ff',
+        Name.Tag:                   'bold #1e90ff',
+        Name.Decorator:             '#888888',
+
+        String:                     '#aa5500',
+        String.Symbol:              '#0000aa',
+        String.Regex:               '#009999',
+
+        Number:                     '#009999',
+
+        Generic.Heading:            'bold #000080',
+        Generic.Subheading:         'bold #800080',
+        Generic.Deleted:            '#aa0000',
+        Generic.Inserted:           '#00aa00',
+        Generic.Error:              '#aa0000',
+        Generic.Emph:               'italic',
+        Generic.Strong:             'bold',
+        Generic.EmphStrong:         'bold italic',
+        Generic.Prompt:             '#555555',
+        Generic.Output:             '#888888',
+        Generic.Traceback:          '#aa0000',
+
+        Error:                      '#F00 bg:#FAA'
+    }