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/cryptography/hazmat/decrepit/__init__.py

@@ -0,0 +1,5 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import annotations

venv/lib/python3.12/site-packages/cryptography/hazmat/decrepit/ciphers/__init__.py

@@ -0,0 +1,5 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import annotations

venv/lib/python3.12/site-packages/cryptography/hazmat/decrepit/ciphers/algorithms.py

@@ -0,0 +1,112 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
+from __future__ import annotations
+
+from cryptography.hazmat.primitives._cipheralgorithm import (
+    BlockCipherAlgorithm,
+    CipherAlgorithm,
+    _verify_key_size,
+)
+
+
+class ARC4(CipherAlgorithm):
+    name = "RC4"
+    key_sizes = frozenset([40, 56, 64, 80, 128, 160, 192, 256])
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+class TripleDES(BlockCipherAlgorithm):
+    name = "3DES"
+    block_size = 64
+    key_sizes = frozenset([64, 128, 192])
+
+    def __init__(self, key: bytes):
+        if len(key) == 8:
+            key += key + key
+        elif len(key) == 16:
+            key += key[:8]
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+# Not actually supported, marker for tests
+class _DES:
+    key_size = 64
+
+
+class Blowfish(BlockCipherAlgorithm):
+    name = "Blowfish"
+    block_size = 64
+    key_sizes = frozenset(range(32, 449, 8))
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+class CAST5(BlockCipherAlgorithm):
+    name = "CAST5"
+    block_size = 64
+    key_sizes = frozenset(range(40, 129, 8))
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+class SEED(BlockCipherAlgorithm):
+    name = "SEED"
+    block_size = 128
+    key_sizes = frozenset([128])
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+class IDEA(BlockCipherAlgorithm):
+    name = "IDEA"
+    block_size = 64
+    key_sizes = frozenset([128])
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8
+
+
+# This class only allows RC2 with a 128-bit key. No support for
+# effective key bits or other key sizes is provided.
+class RC2(BlockCipherAlgorithm):
+    name = "RC2"
+    block_size = 64
+    key_sizes = frozenset([128])
+
+    def __init__(self, key: bytes):
+        self.key = _verify_key_size(self, key)
+
+    @property
+    def key_size(self) -> int:
+        return len(self.key) * 8