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

.agents/phases/todo/01_severity_language/01_severity_module.md

@@ -0,0 +1,61 @@
+# Task 01 — Severity module
+
+**Phase:** `01_severity_language` · **Source:** `TODO.md:5` — "proper green (good), yellow (warn), red (danger) color coding" and `TODO.md:7` — "charge, load, and runtime left to be big, obvious, and color coded"
+**Story:** n/a
+
+## Objective
+
+Move the good/worrying/bad decision out of the browser and into one Python module, so the
+four pages cannot drift into four different opinions about what red means.
+
+Today the thresholds live in call sites: `page-system.js:129` passes `75, 90`,
+`page-system.js:139` and `:144` pass `80, 92`, `page-index.js:89` passes `80, 92`,
+`page-llm.js:195` and `:307` pass `75, 90`, and `Dash.severityFor` (`app.js:105`) defaults
+to `75/90`. That is the drift this task ends.
+
+## Work
+
+1. `src/dashboards/severity.py` (new) —
+   - `THRESHOLDS: dict[str, tuple[float, float]]` keyed by metric name, with the ratified
+     defaults: `cpu.usage_pct` 75/90, `mem.used_pct` 80/92, `disk.used_pct` 80/90,
+     `cpu.temp_c` 75/90, `gpu.busy_pct` 85/95, `gpu.mem_used_pct` 85/95,
+     `llm.kv_cache_usage_pct` 75/90, `ups.charge_pct` 50/20, `ups.battery_runtime` 600/300,
+     `ups.load_pct` 70/90.
+   - `INVERTED: set[str]` — metrics where **lower is worse** (`ups.charge_pct`,
+     `ups.battery_runtime`), so callers cannot get the direction wrong.
+   - `classify(metric: str, value: float | None) -> str | None` returning `ok`, `warn`,
+     `fail`, or `None`. `None` in → `None` out, always.
+   - `attach(metric: str, value: float | None) -> dict` returning
+     `{"value": value, "severity": classify(...)}` for the payload shapes that are plain
+     numbers, and `with_severity(metric, cell)` for payloads that already are
+     `{"value":…, "source":…, "derived":…}` (LLM metrics) — additive, never a rename.
+   - Module docstring stating the two rules: unknown is **not** ok (it is `None`, the page
+     renders `n/a` with no colour), and a threshold exists nowhere else in the app. Ties to
+     the `AGENTS.md` "never invent a number" rule.
+2. `tests/test_severity.py` (new) —
+   - boundaries inclusive on the warn edge (`75 → warn`, `74.9 → ok`), danger edge
+     (`90 → fail`), every metric in the table, both directions for the inverted ones,
+     unknown metric name → `None` (no exception), `None` and `float("nan")` → `None`.
+   - a table sanity test asserting each entry's bounds are ordered correctly for its
+     direction, so a future edit cannot silently invert a metric.
+   - ASSUMPTION: the numbers above were confirmed in chat on 2026-10-16; they match what
+     the call sites already pass, except the two UPS metrics which are new.
+   - ASSUMPTION: the vocabulary is **`ok|warn|fail`**, not `ok|warn|danger` — it is what
+     `dash.css` (`.bar.ok`, `.dot.warn`, `.chip.fail`, `ul.checks li.fail`) and
+     `sources/nut.py`'s `health.checks[].status` already use. The TODO's word "danger" maps
+     to `fail`; do not introduce a synonym for the same colour.
+   - ASSUMPTION: `sources/nut.py`'s existing `health.checks[].status` values are left
+     untouched (additive-only anchor). `severity` is a new field on *values*, computed by
+     this module; `nut.assess()` keeps its own judgement about *conditions*.
+
+## Testing & Quality
+
+- Unit only, no I/O, no fixtures needed.
+- Coverage: **>90%** on `severity.py`.
+
+## Completion Criteria
+
+- [ ] `uv run pytest tests/test_severity.py -v` green
+- [ ] `uv run python -c "from dashboards.severity import classify as c; print(c('cpu.usage_pct',95), c('cpu.usage_pct',60), c('cpu.usage_pct',None), c('ups.charge_pct',15))"` → `fail ok None fail`
+- [ ] `uv run pytest` green overall; `ruff` + `pyright` clean
+- [ ] Nothing else changed yet — this task adds a leaf module and its tests