feat: add mesh network visualizer

- D3.js force-directed graph for real-time mesh visualization
- WebSocket server (mesh-viz-bridge crate) for live updates
- Demo mode with simulated topology
- JSONL file upload for offline analysis
- Optional viz logging in mesh_node forwarding

viz/bridge/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "mesh-viz-bridge"
+version = "0.1.0"
+edition = "2021"
+description = "WebSocket bridge: tails NDJSON mesh viz events to browser clients"
+license = "Apache-2.0 OR MIT"
+
+[dependencies]
+anyhow = "1"
+clap = { version = "4", features = ["derive"] }
+futures-util = "0.3"
+serde_json = "1"
+tokio = { version = "1", features = ["macros", "rt-multi-thread", "signal", "time", "fs", "io-util", "net", "sync"] }
+tokio-tungstenite = "0.26"