Add netwatch, syswatch, diskwatch to System tools

Three sibling read-only diagnostics TUIs in Rust:

- netwatch — network diagnostics with DPI across 13 protocols, eBPF/PKTAP
  process attribution, TCP retransmit analytics, JA4 fingerprinting,
  optional Landlock sandbox, and Flight Recorder incident bundles
- syswatch — system diagnostics across 12 tabs with Timeline scrubber
  and Insights anomaly engine
- diskwatch — disk diagnostics across 8 tabs (devices/volumes/IO/SMART)

All three inserted alphabetically into System tools.