fix(logging): replace structlog with stdlib logging to prevent broken pipe crashes

structlog fails with BrokenPipeError when stdout is redirected (e.g., background
processes, Docker logs). Replace all structlog.get_logger() calls with
logging.getLogger() and convert keyword-style log calls to %-format strings.

Also removes stale Docs/tasks.md (2028 lines) and updates Robot Framework
tests to match current API behavior.

src/server/services/background_loader_service.py

@@ -14,17 +14,16 @@ Key Features:
 from __future__ import annotations
 
 import asyncio
+import logging
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
 from enum import Enum
 from pathlib import Path
 from typing import Any, Dict, List, Optional
 
-import structlog
-
 from src.server.services.websocket_service import WebSocketService
 
-logger = structlog.get_logger(__name__)
+logger = logging.getLogger(__name__)
 
 
 class LoadingStatus(str, Enum):
@@ -121,8 +120,8 @@ class BackgroundLoaderService:
         self._shutdown = False
         
         logger.info(
-            "BackgroundLoaderService initialized",
-            extra={"max_concurrent_loads": max_concurrent_loads}
+            "BackgroundLoaderService initialized max_concurrent_loads=%s",
+            max_concurrent_loads
         )
     
     async def start(self) -> None:
@@ -140,8 +139,8 @@ class BackgroundLoaderService:
             self.worker_tasks.append(worker)
         
         logger.info(
-            "Background workers started",
-            extra={"num_workers": len(self.worker_tasks)}
+            "Background workers started num_workers=%s",
+            len(self.worker_tasks)
         )
     
     async def stop(self) -> None:
@@ -164,8 +163,8 @@ class BackgroundLoaderService:
         for i, result in enumerate(results):
             if isinstance(result, Exception) and not isinstance(result, asyncio.CancelledError):
                 logger.error(
-                    f"Worker {i} stopped with exception",
-                    extra={"exception": str(result)}
+                    "Worker %s stopped with exception exception=%s",
+                    i, str(result)
                 )
         
         self.worker_tasks = []
@@ -202,10 +201,15 @@ class BackgroundLoaderService:
         self.active_tasks[key] = task
         await self.task_queue.put(task)
         
-        logger.info("Added loading task for series: %s", key)
+        import logging
+        _task_logger = logging.getLogger(__name__)
+        _task_logger.info("Added loading task for series: %s", key)
         
         # Broadcast initial status
-        await self._broadcast_status(task)
+        try:
+            await self._broadcast_status(task)
+        except Exception as e:
+            _task_logger.warning("Failed to broadcast initial status: %s", e)
     
     async def check_missing_data(
         self,
@@ -288,7 +292,8 @@ class BackgroundLoaderService:
                 )
                 
                 logger.info(
-                    f"Worker {worker_id} processing loading task for series: {task.key}"
+                    "Worker %s processing loading task for series: %s",
+                    worker_id, task.key
                 )
                 
                 # Process the task
@@ -304,7 +309,10 @@ class BackgroundLoaderService:
                 logger.info("Worker %s task cancelled", worker_id)
                 break
             except Exception as e:
-                logger.exception("Error in background worker %s: %s", worker_id, e)
+                logger.error(
+                    "Error in background worker %s: %s",
+                    worker_id, str(e)
+                )
                 # Continue processing other tasks
                 continue