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/sas.py

@@ -0,0 +1,46 @@
+"""
+    pygments.styles.sas
+    ~~~~~~~~~~~~~~~~~~~
+
+    Style inspired by SAS' enhanced program editor. Note This is not
+    meant to be a complete style. It's merely meant to mimic SAS'
+    program editor syntax highlighting.
+
+    :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, Other, Whitespace, Generic
+
+
+__all__ = ['SasStyle']
+
+
+class SasStyle(Style):
+    """
+    Style inspired by SAS' enhanced program editor. Note This is not
+    meant to be a complete style. It's merely meant to mimic SAS'
+    program editor syntax highlighting.
+    """
+
+    name = 'sas'
+    
+    styles = {
+        Whitespace:            '#bbbbbb',
+        Comment:               'italic #008800',
+        String:                '#800080',
+        Number:                'bold #2c8553',
+        Other:                 'bg:#ffffe0',
+        Keyword:               '#2c2cff',
+        Keyword.Reserved:      'bold #353580',
+        Keyword.Constant:      'bold',
+        Name.Builtin:          '#2c2cff',
+        Name.Function:         'bold italic',
+        Name.Variable:         'bold #2c2cff',
+        Generic:               '#2c2cff',
+        Generic.Emph:          '#008800',
+        Generic.Error:         '#d30202',
+        Error:                 'bg:#e3d2d2 #a61717'
+    }