feat: probe mesh mode + Grafana dashboard (T5-S6/S7) — completes T5
WZP-P2-T5-S6: Probe mesh mode
- ProbeMesh coordinator: wraps multiple ProbeRunners, spawns all concurrently
- mesh_summary(): scans registry, formats human-readable health table
- /mesh HTTP endpoint on metrics port alongside /metrics
- --probe-mesh flag, --mesh-status for CLI diagnostics
- Replaces individual probe spawn loop with ProbeMesh::run_all()
- 4 tests: mesh creation, empty/populated summary, zero targets
WZP-P2-T5-S7: Grafana dashboard
- docs/grafana-dashboard.json — importable directly into Grafana
- Row 1: Relay Health (sessions, rooms, packets/s, bytes/s, auth, handshake)
- Row 2: Call Quality (buffer depth, loss%, RTT, underruns per session)
- Row 3: Inter-Relay Mesh (RTT heatmap, loss, jitter, probe up/down)
- Row 4: Web Bridge (connections, frames bridged, auth failures, latency)
- Datasource variable ${DS_PROMETHEUS}, auto-refresh 10s
- Color thresholds: loss 2%/5%, RTT 100ms/300ms, probe up=green/down=red
T5 Telemetry & Observability is now COMPLETE (all 7 subtasks).
235 tests passing across all crates.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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