feat: v1.2.0-alpha — E2E encrypted mesh relay, steganography, relay status polling

Phase 5 mesh networking:
- E2E encrypted TX relay (X25519 + ChaCha20-Poly1305) — non-Archy nodes
  relay encrypted blobs transparently via Meshcore native routing
- Steganographic encoding modes (WeatherStation, SensorNetwork) — traffic
  looks like sensor data on the wire, 0xAA marker, configurable per-node
- Pre-flight Bitcoin Core health check on relay node — specific error codes
  (bitcoin_unreachable, bitcoin_syncing, tx_rejected) instead of generic fails
- mesh.relay-status RPC endpoint — frontend polls for relay result every 3s
- On-Chain / Lightning tabs in Off-Grid Bitcoin panel
- Archy Peers vs Mesh Broadcast relay mode selector
- Mesh view fills viewport (no page scroll), internal panel scrolling
- Version bump to 1.2.0-alpha

Also includes: deploy hardening, container fixes, IndeedHub updates,
boot screen, dashboard improvements, MASTER_PLAN task tracking

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/Cargo.lock

@@ -101,6 +101,7 @@ dependencies = [
  "flate2",
  "futures-util",
  "hex",
+ "hkdf",
  "hmac",
  "http-body 1.0.1",
  "http-body-util",
@@ -1058,6 +1059,15 @@ dependencies = [
  "arrayvec",
 ]
 
+[[package]]
+name = "hkdf"
+version = "0.12.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7b5f8eb2ad728638ea2c7d47a21db23b7b58a72ed6a38256b8a1849f15fbbdf7"
+dependencies = [
+ "hmac",
+]
+
 [[package]]
 name = "hmac"
 version = "0.12.1"