refactor: v0.2.1 refinements — HttpClient lifetime, disconnection UX, DataGrid
Post-v0.2 polish (no behavior regressions; 127 tests + 2 docker integration green).
- MTConnect: shared static HttpClient (Timeout=Infinite) + per-request timeout
via linked CancellationTokenSource. Fixes socket-exhaustion risk from
new-HttpClient-per-driver on config edits / dynamic monitor reload.
- Disconnection UX: dashboard + detail show connection state with color
(green/red/grey dot + badge) via StatusKindToBrush converter; LastSeen
timestamp preserved across disconnects. VMs stay framework-agnostic.
- Delete confirm: VM-driven overlay naming the machine (replaces two-state
button) to prevent accidental deletion.
- Dashboard table: switched to DataGrid — aligned columns + Details gets its
own column (fixes row misalignment). Adds Avalonia.Controls.DataGrid 11.3.10.
PAUL: roadmap re-sequenced — v0.3 Data-Item Selection + UX, OPC UA → v0.4,
Fanuc → v0.5, History → v0.6.
Touches: Junction.Protocols.MTConnect, Junction.App, tests, .paul/.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>