fix: pipeline stop now halts all workers and flushes queues

Workers (ingestion, parser, extractor, aggregation, recommendation,
broker, lake-publisher) now check the pipeline:enabled Redis flag on
each loop iteration and sleep when disabled.

The toggle endpoint flushes all pipeline queues on disable so queued
jobs don't resume when workers eventually check. Broker/trading queues
are excluded from flush to avoid dropping in-flight orders.

services/scheduler/app.py

@@ -20,7 +20,7 @@ from services.shared.config import load_config
 from services.shared.db import get_pg_pool, get_redis
 from services.shared.logging import setup_logging
 from services.shared.redis_keys import (
-    PREFIX,
+    PIPELINE_ENABLED_KEY,
     QUEUE_EXTRACTION,
     QUEUE_INGESTION,
     QUEUE_MACRO_CLASSIFICATION,
@@ -501,7 +501,7 @@ async def main() -> None:
     rds = get_redis(config)
 
     logger.info("Scheduler started (tick=%ds)", SCHEDULER_TICK)
-    pipeline_key = f"{PREFIX}:pipeline:enabled"
+    pipeline_key = PIPELINE_ENABLED_KEY
 
     # If PIPELINE_DEFAULT_OFF is set, initialize the toggle to OFF on first boot
     # (only if the key doesn't already exist — preserves manual overrides)