feat(kerykeion): gateway bridge, MQTT parsing, collector run loop, and mesh CLI

[forkwright]

Summary

• GatewayBridge (bridge.rs): multi-gateway selection by priority and health rank, automatic failover with 30s cooldown, health monitoring with Healthy → Degraded → Offline state transitions, periodic health check loop with CancellationToken shutdown
• MQTT message parsing (mqtt.rs): decode ServiceEnvelope, MapReport, and MqttClientProxyMessage protobuf envelopes; extract gateway info from !hex gateway ID strings; lat/lon conversion from fixed-point integers
• MeshCollector run loop (collector.rs): transport connection, config handshake, heartbeat and health monitor background task spawning via JoinSet, main receive loop with biased tokio::select!, graceful shutdown draining all tasks
• Mesh CLI (mesh/mod.rs): akroasis mesh status, mesh nodes, mesh send, mesh topology subcommands with comfy-table formatted output; live-data helpers (build_status_table, build_nodes_table, format_node_row, format_gateway_health) for daemon integration
• Integration wiring: MQTT proto compilation, module declarations, lib.rs re-exports, CLI registration, akroasis → kerykeion dependency

Test plan

• 48 new tests: bridge (12), mqtt (10), collector (11), mesh CLI (15)
• cargo fmt --all -- --check clean
• cargo clippy --workspace --all-targets -- -D warnings clean
• cargo test --workspace — 462 tests pass, 0 failures
• cargo test --workspace --doc clean

Validation gate

cargo fmt --all -- --check    ✓
cargo clippy --workspace --all-targets -- -D warnings    ✓
cargo test --workspace    ✓ (462 passed)

[github-actions]

⚠️ Large PR detected — 12 files, 1797 lines changed.

Consider splitting into smaller PRs for easier review. Not a blocker, just a signal.