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>

core/archipelago/src/mesh/protocol.rs

@@ -408,6 +408,78 @@ pub fn parse_channel_msg_v1(data: &[u8]) -> Result<(u8, String)> {
     Ok((channel_idx, text))
 }
 
+// ─── Raw-bytes variants for typed message detection ────────────────────
+
+/// Parse RESP_CONTACT_MSG_V3 returning raw payload bytes (not UTF-8 lossy).
+/// Returns (sender_pubkey_prefix_hex, raw_payload_bytes, snr).
+pub fn parse_contact_msg_v3_raw(data: &[u8]) -> Result<(String, Vec<u8>, i8)> {
+    if data.len() < 15 {
+        anyhow::bail!("Contact message too short: {} bytes", data.len());
+    }
+    let snr = data[0] as i8;
+    let pubkey_prefix = hex::encode(&data[3..9]);
+    let txt_type = data[10];
+    let text_start = if txt_type == 2 { 19 } else { 15 };
+    let payload = if data.len() > text_start {
+        data[text_start..].to_vec()
+    } else {
+        Vec::new()
+    };
+    Ok((pubkey_prefix, payload, snr))
+}
+
+/// Parse RESP_CONTACT_MSG returning raw payload bytes.
+/// Returns (sender_pubkey_prefix_hex, raw_payload_bytes).
+pub fn parse_contact_msg_v1_raw(data: &[u8]) -> Result<(String, Vec<u8>)> {
+    if data.len() < 12 {
+        anyhow::bail!("Contact message v1 too short: {} bytes", data.len());
+    }
+    let pubkey_prefix = hex::encode(&data[0..6]);
+    let txt_type = data[7];
+    let text_start = if txt_type == 2 { 16 } else { 12 };
+    let payload = if data.len() > text_start {
+        data[text_start..].to_vec()
+    } else {
+        Vec::new()
+    };
+    Ok((pubkey_prefix, payload))
+}
+
+/// Parse RESP_CHANNEL_MSG_V3 returning raw payload bytes.
+/// Returns (channel_idx, raw_payload_bytes).
+pub fn parse_channel_msg_v3_raw(data: &[u8]) -> Result<(u8, Vec<u8>)> {
+    if data.len() < 7 {
+        anyhow::bail!("Channel message too short: {} bytes", data.len());
+    }
+    let channel_idx = data[0];
+    let payload = if data.len() > 7 {
+        let mut p = data[7..].to_vec();
+        // Strip trailing NUL bytes
+        while p.last() == Some(&0) { p.pop(); }
+        p
+    } else {
+        Vec::new()
+    };
+    Ok((channel_idx, payload))
+}
+
+/// Parse RESP_CHANNEL_MSG returning raw payload bytes.
+/// Returns (channel_idx, raw_payload_bytes).
+pub fn parse_channel_msg_v1_raw(data: &[u8]) -> Result<(u8, Vec<u8>)> {
+    if data.len() < 7 {
+        anyhow::bail!("Channel message v1 too short: {} bytes", data.len());
+    }
+    let channel_idx = data[0];
+    let payload = if data.len() > 7 {
+        let mut p = data[7..].to_vec();
+        while p.last() == Some(&0) { p.pop(); }
+        p
+    } else {
+        Vec::new()
+    };
+    Ok((channel_idx, payload))
+}
+
 /// Parse RESP_ERR (0x01). Returns descriptive error string.
 pub fn parse_error(data: &[u8]) -> String {
     if data.is_empty() {