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/yaml/dumper.py

@@ -0,0 +1,62 @@
+
+__all__ = ['BaseDumper', 'SafeDumper', 'Dumper']
+
+from .emitter import *
+from .serializer import *
+from .representer import *
+from .resolver import *
+
+class BaseDumper(Emitter, Serializer, BaseRepresenter, BaseResolver):
+
+    def __init__(self, stream,
+            default_style=None, default_flow_style=False,
+            canonical=None, indent=None, width=None,
+            allow_unicode=None, line_break=None,
+            encoding=None, explicit_start=None, explicit_end=None,
+            version=None, tags=None, sort_keys=True):
+        Emitter.__init__(self, stream, canonical=canonical,
+                indent=indent, width=width,
+                allow_unicode=allow_unicode, line_break=line_break)
+        Serializer.__init__(self, encoding=encoding,
+                explicit_start=explicit_start, explicit_end=explicit_end,
+                version=version, tags=tags)
+        Representer.__init__(self, default_style=default_style,
+                default_flow_style=default_flow_style, sort_keys=sort_keys)
+        Resolver.__init__(self)
+
+class SafeDumper(Emitter, Serializer, SafeRepresenter, Resolver):
+
+    def __init__(self, stream,
+            default_style=None, default_flow_style=False,
+            canonical=None, indent=None, width=None,
+            allow_unicode=None, line_break=None,
+            encoding=None, explicit_start=None, explicit_end=None,
+            version=None, tags=None, sort_keys=True):
+        Emitter.__init__(self, stream, canonical=canonical,
+                indent=indent, width=width,
+                allow_unicode=allow_unicode, line_break=line_break)
+        Serializer.__init__(self, encoding=encoding,
+                explicit_start=explicit_start, explicit_end=explicit_end,
+                version=version, tags=tags)
+        SafeRepresenter.__init__(self, default_style=default_style,
+                default_flow_style=default_flow_style, sort_keys=sort_keys)
+        Resolver.__init__(self)
+
+class Dumper(Emitter, Serializer, Representer, Resolver):
+
+    def __init__(self, stream,
+            default_style=None, default_flow_style=False,
+            canonical=None, indent=None, width=None,
+            allow_unicode=None, line_break=None,
+            encoding=None, explicit_start=None, explicit_end=None,
+            version=None, tags=None, sort_keys=True):
+        Emitter.__init__(self, stream, canonical=canonical,
+                indent=indent, width=width,
+                allow_unicode=allow_unicode, line_break=line_break)
+        Serializer.__init__(self, encoding=encoding,
+                explicit_start=explicit_start, explicit_end=explicit_end,
+                version=version, tags=tags)
+        Representer.__init__(self, default_style=default_style,
+                default_flow_style=default_flow_style, sort_keys=sort_keys)
+        Resolver.__init__(self)
+