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>

CHANGELOG.md

@@ -5,6 +5,14 @@ All notable changes to RigDoctor are recorded here. Format follows
 (`MAJOR.MINOR.PATCH`, pre-1.0). `__version__` and `pyproject.toml` must match the git
 release tag (so the auto-updater, D18, can compare versions).
 
+## [0.21.0] - 2026-05-22
+### Added
+- **Live monitor TUI (M2).** `rigdoctor monitor` is now a proper **curses** dashboard:
+  current / session-min / session-max per sensor, grouped by subsystem, with temperature and
+  utilization **color bands** (and GPU-lost flagged red). `q` quits, `r` resets the session
+  min/max. Falls back to a plain full-screen redraw on a non-TTY (`--plain` forces it). The
+  terminal face of the same live data the GUI dashboard graphs. Completes the Monitoring bundle.
+
 ## [0.20.0] - 2026-05-22
 ### Changed
 - **Reorganized navigation** into grouped sidebar sections — **Monitor** (Dashboard) ·