feat: implement pngx-controller with Gitea CI/CD deployment

- Full FastAPI sync engine: master→replica document sync via paperless REST API
- Web UI: dashboard, replicas, logs, settings (Jinja2 + HTMX + Pico CSS)
- APScheduler background sync, SSE live log stream, Prometheus metrics
- Fernet encryption for API tokens at rest
- pngx.env credential file: written on save, pre-fills forms on load
- Dockerfile with layer-cached uv build, Python healthcheck
- docker-compose with host networking for Tailscale access
- Gitea Actions workflow: version bump, secret injection, docker compose deploy

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

app/scheduler.py

@@ -0,0 +1,63 @@
+import asyncio
+
+from apscheduler.schedulers.asyncio import AsyncIOScheduler
+
+_scheduler: AsyncIOScheduler | None = None
+
+SETTINGS_DEFAULTS = {
+    "sync_interval_seconds": "900",
+    "log_retention_days": "90",
+    "sync_cycle_timeout_seconds": "1800",
+    "task_poll_timeout_seconds": "600",
+    "replica_suspend_threshold": "5",
+    "max_concurrent_requests": "4",
+    "alert_target_type": "",
+    "alert_target_url": "",
+    "alert_target_token": "",
+    "alert_error_threshold": "5",
+    "alert_cooldown_seconds": "3600",
+}
+
+
+def get_setting(settings: dict, key: str) -> str:
+    return settings.get(key) or SETTINGS_DEFAULTS.get(key, "")
+
+
+def get_setting_int(settings: dict, key: str) -> int:
+    return int(get_setting(settings, key) or SETTINGS_DEFAULTS[key])
+
+
+async def _sync_job() -> None:
+    from .sync.engine import run_sync_cycle
+
+    await run_sync_cycle(triggered_by="scheduler")
+
+
+def start_scheduler(interval_seconds: int = 900) -> AsyncIOScheduler:
+    global _scheduler
+    _scheduler = AsyncIOScheduler()
+    _scheduler.add_job(
+        _sync_job,
+        "interval",
+        seconds=interval_seconds,
+        id="sync_job",
+        replace_existing=True,
+        max_instances=1,
+    )
+    _scheduler.start()
+    return _scheduler
+
+
+def reschedule(interval_seconds: int) -> None:
+    if _scheduler is None:
+        return
+    _scheduler.reschedule_job(
+        "sync_job",
+        trigger="interval",
+        seconds=interval_seconds,
+    )
+
+
+def stop_scheduler() -> None:
+    if _scheduler:
+        _scheduler.shutdown(wait=False)