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/PIL/_binary.py

@@ -0,0 +1,113 @@
+#
+# The Python Imaging Library.
+# $Id$
+#
+# Binary input/output support routines.
+#
+# Copyright (c) 1997-2003 by Secret Labs AB
+# Copyright (c) 1995-2003 by Fredrik Lundh
+# Copyright (c) 2012 by Brian Crowell
+#
+# See the README file for information on usage and redistribution.
+#
+
+
+"""Binary input/output support routines."""
+
+from __future__ import annotations
+
+from struct import pack, unpack_from
+
+
+def i8(c: bytes) -> int:
+    return c[0]
+
+
+def o8(i: int) -> bytes:
+    return bytes((i & 255,))
+
+
+# Input, le = little endian, be = big endian
+def i16le(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 2-bytes (16 bits) string to an unsigned integer.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from("<H", c, o)[0]
+
+
+def si16le(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 2-bytes (16 bits) string to a signed integer.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from("<h", c, o)[0]
+
+
+def si16be(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 2-bytes (16 bits) string to a signed integer, big endian.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from(">h", c, o)[0]
+
+
+def i32le(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 4-bytes (32 bits) string to an unsigned integer.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from("<I", c, o)[0]
+
+
+def si32le(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 4-bytes (32 bits) string to a signed integer.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from("<i", c, o)[0]
+
+
+def si32be(c: bytes, o: int = 0) -> int:
+    """
+    Converts a 4-bytes (32 bits) string to a signed integer, big endian.
+
+    :param c: string containing bytes to convert
+    :param o: offset of bytes to convert in string
+    """
+    return unpack_from(">i", c, o)[0]
+
+
+def i16be(c: bytes, o: int = 0) -> int:
+    return unpack_from(">H", c, o)[0]
+
+
+def i32be(c: bytes, o: int = 0) -> int:
+    return unpack_from(">I", c, o)[0]
+
+
+# Output, le = little endian, be = big endian
+def o16le(i: int) -> bytes:
+    return pack("<H", i)
+
+
+def o32le(i: int) -> bytes:
+    return pack("<I", i)
+
+
+def o16be(i: int) -> bytes:
+    return pack(">H", i)
+
+
+def o32be(i: int) -> bytes:
+    return pack(">I", i)