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/tenacity/asyncio/retry.py

@@ -0,0 +1,125 @@
+# Copyright 2016–2021 Julien Danjou
+# Copyright 2016 Joshua Harlow
+# Copyright 2013-2014 Ray Holder
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+import abc
+import typing
+
+from tenacity import _utils
+from tenacity import retry_base
+
+if typing.TYPE_CHECKING:
+    from tenacity import RetryCallState
+
+
+class async_retry_base(retry_base):
+    """Abstract base class for async retry strategies."""
+
+    @abc.abstractmethod
+    async def __call__(self, retry_state: "RetryCallState") -> bool:  # type: ignore[override]
+        pass
+
+    def __and__(  # type: ignore[override]
+        self, other: "typing.Union[retry_base, async_retry_base]"
+    ) -> "retry_all":
+        return retry_all(self, other)
+
+    def __rand__(  # type: ignore[misc,override]
+        self, other: "typing.Union[retry_base, async_retry_base]"
+    ) -> "retry_all":
+        return retry_all(other, self)
+
+    def __or__(  # type: ignore[override]
+        self, other: "typing.Union[retry_base, async_retry_base]"
+    ) -> "retry_any":
+        return retry_any(self, other)
+
+    def __ror__(  # type: ignore[misc,override]
+        self, other: "typing.Union[retry_base, async_retry_base]"
+    ) -> "retry_any":
+        return retry_any(other, self)
+
+
+RetryBaseT = typing.Union[
+    async_retry_base, typing.Callable[["RetryCallState"], typing.Awaitable[bool]]
+]
+
+
+class retry_if_exception(async_retry_base):
+    """Retry strategy that retries if an exception verifies a predicate."""
+
+    def __init__(
+        self, predicate: typing.Callable[[BaseException], typing.Awaitable[bool]]
+    ) -> None:
+        self.predicate = predicate
+
+    async def __call__(self, retry_state: "RetryCallState") -> bool:  # type: ignore[override]
+        if retry_state.outcome is None:
+            raise RuntimeError("__call__() called before outcome was set")
+
+        if retry_state.outcome.failed:
+            exception = retry_state.outcome.exception()
+            if exception is None:
+                raise RuntimeError("outcome failed but the exception is None")
+            return await self.predicate(exception)
+        else:
+            return False
+
+
+class retry_if_result(async_retry_base):
+    """Retries if the result verifies a predicate."""
+
+    def __init__(
+        self, predicate: typing.Callable[[typing.Any], typing.Awaitable[bool]]
+    ) -> None:
+        self.predicate = predicate
+
+    async def __call__(self, retry_state: "RetryCallState") -> bool:  # type: ignore[override]
+        if retry_state.outcome is None:
+            raise RuntimeError("__call__() called before outcome was set")
+
+        if not retry_state.outcome.failed:
+            return await self.predicate(retry_state.outcome.result())
+        else:
+            return False
+
+
+class retry_any(async_retry_base):
+    """Retries if any of the retries condition is valid."""
+
+    def __init__(self, *retries: typing.Union[retry_base, async_retry_base]) -> None:
+        self.retries = retries
+
+    async def __call__(self, retry_state: "RetryCallState") -> bool:  # type: ignore[override]
+        result = False
+        for r in self.retries:
+            result = result or await _utils.wrap_to_async_func(r)(retry_state)
+            if result:
+                break
+        return result
+
+
+class retry_all(async_retry_base):
+    """Retries if all the retries condition are valid."""
+
+    def __init__(self, *retries: typing.Union[retry_base, async_retry_base]) -> None:
+        self.retries = retries
+
+    async def __call__(self, retry_state: "RetryCallState") -> bool:  # type: ignore[override]
+        result = True
+        for r in self.retries:
+            result = result and await _utils.wrap_to_async_func(r)(retry_state)
+            if not result:
+                break
+        return result