chore: bootstrap repository with governance docs

Initialize git, add Apache-2.0 LICENSE, .gitattributes (LF line
endings), AGENTS.md (entry points, stack, discovery order, baseline
checks), RUNBOOK.md (dev boot, prod deploy with overlay, ingestion,
failures, rollback, scaling notes), .env.prod.example with rotated
credential placeholders, and dev-only warnings on .env.example.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/workers/celery_app.py

@@ -0,0 +1,28 @@
+"""Celery application instance."""
+
+from __future__ import annotations
+
+from celery import Celery
+
+from app.config import settings
+from app.logging_config import configure_logging
+
+configure_logging()
+
+celery_app = Celery(
+    "legacyhub",
+    broker=settings.redis_url,
+    backend=settings.redis_url,
+    include=["app.workers.tasks"],
+)
+
+celery_app.conf.update(
+    task_acks_late=True,
+    task_reject_on_worker_lost=True,
+    task_track_started=True,
+    worker_prefetch_multiplier=1,
+    task_time_limit=settings.max_document_timeout_seconds * 4,
+    task_soft_time_limit=settings.max_document_timeout_seconds * 3,
+    timezone="UTC",
+    enable_utc=True,
+)