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/lexers/asc.py

@@ -0,0 +1,55 @@
+"""
+    pygments.lexers.asc
+    ~~~~~~~~~~~~~~~~~~~
+
+    Lexer for various ASCII armored files.
+
+    :copyright: Copyright 2006-present by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+import re
+
+from pygments.lexer import RegexLexer, bygroups
+from pygments.token import Comment, Generic, Name, Operator, String, Whitespace
+
+__all__ = ['AscLexer']
+
+
+class AscLexer(RegexLexer):
+    """
+    Lexer for ASCII armored files, containing `-----BEGIN/END ...-----` wrapped
+    base64 data.
+    """
+    name = 'ASCII armored'
+    aliases = ['asc', 'pem']
+    filenames = [
+        '*.asc',  # PGP; *.gpg, *.pgp, and *.sig too, but those can be binary
+        '*.pem',  # X.509; *.cer, *.crt, *.csr, and key etc too, but those can be binary
+        'id_dsa', 'id_ecdsa', 'id_ecdsa_sk', 'id_ed25519', 'id_ed25519_sk',
+        'id_rsa',  # SSH private keys
+    ]
+    mimetypes = ['application/pgp-keys', 'application/pgp-encrypted',
+                 'application/pgp-signature', 'application/pem-certificate-chain']
+    url = 'https://www.openpgp.org'
+    version_added = '2.10'
+
+    flags = re.MULTILINE
+
+    tokens = {
+        'root': [
+            (r'\s+', Whitespace),
+            (r'^-----BEGIN [^\n]+-----$', Generic.Heading, 'data'),
+            (r'\S+', Comment),
+        ],
+        'data': [
+            (r'\s+', Whitespace),
+            (r'^([^:]+)(:)([ \t]+)(.*)',
+             bygroups(Name.Attribute, Operator, Whitespace, String)),
+            (r'^-----END [^\n]+-----$', Generic.Heading, 'root'),
+            (r'\S+', String),
+        ],
+    }
+
+    def analyse_text(text):
+        if re.search(r'^-----BEGIN [^\n]+-----\r?\n', text):
+            return True