feat: Phase 4 — off-grid Bitcoin relay, block headers, dead man's switch
- Typed message dispatch in listener (BlockHeader, TxRelay, LightningRelay, Alert, TxConfirmation)
- Base64 encoding for binary payloads over LoRa (fixes NUL byte truncation)
- Compact block header announcements (88 bytes, fits 160-byte LoRa limit)
- Block header announcer: internet nodes auto-announce new blocks to Archy peers
- TX relay: mesh-only nodes can broadcast transactions via internet-connected peers
- Confirmation tracking: relay node monitors 1/3, 2/3, 3/3 confirmations, sends updates back
- Dead man's switch background task with configurable interval and signed alert broadcast
- 6 new RPC endpoints: relay-tx, block-headers, relay-lightning, deadman-status/configure/checkin
- lnd.create-raw-tx: create signed TX without broadcasting (for mesh relay)
- Web5 wallet: offline detection + "Send via mesh?" prompt with auto relay + confirmation polling
- Mesh.vue: Off-Grid Bitcoin tab, Dead Man tab, Send Bitcoin/Lightning buttons
- TX/Lightning relay sends only to Archy peers (not broadcast to all devices)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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