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/uvloop/includes/consts.pxi

@@ -0,0 +1,33 @@
+cdef enum:
+    UV_STREAM_RECV_BUF_SIZE = 256000  # 250kb
+
+    FLOW_CONTROL_HIGH_WATER = 64  # KiB
+    FLOW_CONTROL_HIGH_WATER_SSL_READ = 256  # KiB
+    FLOW_CONTROL_HIGH_WATER_SSL_WRITE = 512  # KiB
+
+    DEFAULT_FREELIST_SIZE = 250
+    DNS_PYADDR_TO_SOCKADDR_CACHE_SIZE = 2048
+
+    DEBUG_STACK_DEPTH = 10
+
+
+    __PROCESS_DEBUG_SLEEP_AFTER_FORK = 1
+
+
+    LOG_THRESHOLD_FOR_CONNLOST_WRITES = 5
+    SSL_READ_MAX_SIZE = 256 * 1024
+
+
+cdef extern from *:
+    '''
+    // Number of seconds to wait for SSL handshake to complete
+    // The default timeout matches that of Nginx.
+    #define SSL_HANDSHAKE_TIMEOUT 60.0
+
+    // Number of seconds to wait for SSL shutdown to complete
+    // The default timeout mimics lingering_time
+    #define SSL_SHUTDOWN_TIMEOUT 30.0
+    '''
+
+    const float SSL_HANDSHAKE_TIMEOUT
+    const float SSL_SHUTDOWN_TIMEOUT