fix: fable_add_task_log sends content not body to match API

The MCP tool was sending {"body": ...} but the task logs API route
expects {"content": ...}, causing 400 errors.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

fable-mcp/fable_mcp/server.py

@@ -298,7 +298,7 @@ async def fable_update_task(
 
 
 @mcp.tool()
-async def fable_add_task_log(task_id: int, body: str) -> dict:
+async def fable_add_task_log(task_id: int, content: str) -> dict:
     """Append a timestamped progress log entry to a Fable task.
 
     Use this to record work sessions, decisions, or status updates over time without
@@ -306,7 +306,7 @@ async def fable_add_task_log(task_id: int, body: str) -> dict:
     chronologically in the task view.
     """
     async with FableClient() as client:
-        return await tasks.add_task_log(client, task_id=task_id, body=body)
+        return await tasks.add_task_log(client, task_id=task_id, content=content)
 
 
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