feat(hub): add Bark notification channel

[xxbbzy]

Summary

• add Bark notification delivery client with timeout and single retry for transient failures
• add Bark notification channel and wire it into hub notification startup flow
• add Bark configuration loading, source tracking, and startup logging
• document new env vars in hub README
• add tests for Bark delivery/channel plus notification hub channel-failure isolation

Detailed Operations

1. Added Bark config fields in settings + server settings loaders (BARK_DEVICE_KEY, BARK_SERVER_URL) and propagated them through Configuration.
2. Logged Bark enablement + server URL source during hub startup.
3. Implemented BarkDelivery for HTTP POST /push with timeout and retry behavior.
4. Implemented BarkNotificationChannel + factory, including session URL building from publicUrl.
5. Registered Bark channel in hub startup so it is enabled only when a device key is configured.
6. Added unit tests for delivery behavior, channel payload mapping, URL path-prefix handling, and multi-channel failure isolation in NotificationHub.

Verification

• Could not run tests in this execution environment: bun is not installed (/usr/bin/bash: bun: command not found).

Notes

• Branch: feat-bark-notifications
• Commit: 1e1d681

[github-actions]

Findings

• None.

Summary

• Review mode: initial. No issues found in the diff. Residual risks/testing gaps: behavior against a real Bark server endpoint is unverified in this review; only unit-level coverage appears in the diff.

Testing

• Not run (automation)