chore(agent): phase roadmap from TODO.md, 5 phases

The five UI items in TODO.md become an executable pipeline. Planning files
only — no application code changed.

- 01_severity_language: one Python threshold table + `severity` on the
  values the pages colour, plus the .hero style. Today the thresholds are
  magic numbers at six JS call sites (75/90 here, 80/92 there), which is
  exactly how "same colour, four meanings" happens.
- 02_overview_fleet_and_alerts: /api/summary gains a derived `alerts`
  list; the page drops to fleet + warnings. Unconfigured sources must not
  alert — that is invariant 3, tested.
- 03_system_per_host_panels: per-host hero cards, no per-core, shared
  multi-host charts and the detail picker deleted. The six card metrics
  already exist in the payload, so the first task pins them with tests
  instead of inventing fields.
- 04_llm_chart_readability: charts.js already exports sparkline() and no
  page calls it — that is why the page reads flat. Port llm_monitor's
  drawSpark behaviour (fixed max, right growth, p95 foots) and keep the
  provenance tags.
- 05_ups_hero_battery_glyph: charge/load/runtime hero + an SVG battery
  whose fill is the charge, verified against both real UPSes and the
  low-charge/on-battery states only the simulator can produce.

PLAN.md records the ratified anchors and the deviation worth knowing:
severity vocabulary is ok|warn|fail, matching dash.css and nut.py, not the
"danger" wording in the proposal — one synonym for one colour.

TODO.md cleared to a bare heading; the items are now phases. .gitignore
stops ignoring all of .agents/ (the roadmap is project history) while
keeping phase-sessions/ and pipeline.log out. deploy/nut-sudoers rewritten:
its header still blamed a port mystery that is solved; the remaining need
is reading upsd.users so adding a scoped dashboards user does not delete
the accounts upsmon authenticates as.

LLM-Generated: true

.gitignore

@@ -31,9 +31,10 @@ agent/*.tar.gz
 .idea/
 .DS_Store
 
-# Agent/pipeline scratch. This project's plan lives in AGENTS.md (tracked) — nothing under
-# .agents/ is anything another checkout needs, so all of it stays out.
-.agents/
+# Agent/pipeline scratch ONLY. The planning tree (.agents/PLAN.md, .agents/phases/) is
+# tracked on purpose — it is the project's roadmap and history, not throwaway state.
+.agents/phase-sessions/
+.agents/pipeline.log
 
 # The original brief for this project. Kept in the checkout as local context, not history:
 # README.md and AGENTS.md carry the decisions that came out of it.