feat: live monitor TUI (M2) — 0.21.0

Upgrade `rigdoctor monitor` from a basic redraw to a stdlib curses dashboard
(tui.py): current / session-min / session-max per sensor, grouped by subsystem,
with temperature & utilization color bands (GPU-lost flagged red). q quits,
r resets min/max. Plain full-screen redraw fallback on a non-TTY (--plain forces
it). Pure track()/band() helpers are unit-tested; curses path verified in a pty.

Completes the Monitoring bundle (M2 + M8).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "rigdoctor"
-version = "0.20.0"
+version = "0.21.0"
 description = "Modular hardware monitoring & crash diagnostics for Linux gamers."
 readme = "README.md"
 requires-python = ">=3.11"