refactor: Use modern Python type alias for StringOrInt in build_context

Replace Union[int, str] with cleaner StringOrInt type alias using modern
Python 3.12+ type statement syntax. This improves code readability while
maintaining the same functionality for string-to-integer conversion in
the depth parameter.

Changes:
- Add StringOrInt type alias using modern type statement
- Update depth parameter annotation to use StringOrInt
- Maintains all existing string conversion and validation logic

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>
Signed-off-by: Joe P <joe@basicmemory.com>

Author: jope-bm

src/basic_memory/mcp/tools/build_context.py

@@ -15,6 +15,7 @@
     memory_url_path,
 )
 
+type StringOrInt = str | int
 
 @mcp.tool(
     description="""Build context from a memory:// URI to continue conversations naturally.
@@ -35,7 +36,7 @@
 )
 async def build_context(
     url: MemoryUrl,
-    depth: Optional[Union[int, str]] = 1,
+    depth: Optional[StringOrInt] = 1,
     timeframe: Optional[TimeFrame] = "7d",
     page: int = 1,
     page_size: int = 10,