Readiness score: detail screen with contributor breakdown and trend (3/5) - #108

Second readiness PR (saksham2001#103), building on the scoring engine. Puts the score
on screen as a full-width card pinned directly under the Today hero, above
the metric grid, with its own Settings page.

Deliberately NOT a tile in the reorderable grid. Every other tile reports
one measurement; readiness is a verdict *over* those measurements - HRV,
resting HR, sleep, temperature and yesterday's load collapsed into a single
number. Placing it beside a peer tile framed it as a sibling metric, which
is the wrong mental model, and half a tile's width could not carry the
reasoning that stops it being a black box. So it carries no MetricKey at
all: it is pinned by design, and visibility is the Settings toggle's job
rather than the drag tray's.

The width earns its keep. The card shows the score, its band, the share of
signals it is based on, and the top two contributors holding it back - each
with its own explanation and what it cost, e.g. "Skin temperature 0.5 °C
above your baseline, −3.4 pts".

The empty state counts down instead of repeating an instruction. Readiness
cannot say anything until it knows what *your* normal looks like, and a flat
"wear your ring overnight" gives no sense of whether that means one more
night or two more weeks - on a device with a month of history it reads as
broken. The card now shows a filling ring with "3 of 7 nights" and "4 more
nights to go", so the feature visibly works before it can produce a score.

Progress counts nights that actually produced overnight signal, not days
since install: someone who wore the ring twice in a month is two nights
along, and saying otherwise would promise a score that isn't coming. A night
whose sleep decode failed still counts if vitals were captured. And because
nights are a proxy for BaselineStats.isEstablished - which also requires
enough individual readings - the copy never claims "0 more nights" while
still showing no score; it says it is still gathering readings. A test pins
the advertised night count against the gate itself, so the countdown cannot
drift from what actually unblocks a score.

This also fixes a real gap the previous copy had: it keyed off the pairing
calibration state, so a long-established user who simply lacked a readiness
baseline saw a bare "No score yet" with no path forward.

The card is gated on its master toggle plus "can this ring measure recovery
at all" - HRV or sleep, the two signals ReadinessScore requires. A ring with
neither could never produce a score, so the card is absent rather than
permanently empty.

Band zones live in ReadinessZones rather than on a view, because the card,
the detail hero and the trend chart all need them and none should depend on
another's type name. A test pins them against ReadinessScore.band.

TodayStore needed two changes. ReadinessService.refreshIfStale runs BEFORE
the signature is captured, not after - otherwise the write lands after the
snapshot and forces a second, wasted rebuild. And the signature gained a
readiness clause; without it a freshly scored night sits in the database
while the card keeps showing yesterday's.

Progress is computed only while there is no score, so it never runs on the
happy path.

Also adds an -openReadinessSettings launch arg, matching the existing
nutrition test tooling.

25 new tests. Layout verified in the simulator against seeded demo data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Two inline contributor JSON literals ran past 200 characters, which is
SwiftLint's error threshold and was failing CI. Hoist both into named
multiline constants, matching how the other readiness tests already
carry their fixtures.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Third readiness PR (saksham2001#103). The tile can only name the single biggest drag;
this screen accounts for every contributor, so a user can reconstruct the
arithmetic behind the number. That is what "documented metrics, no black
boxes" has to mean in practice.

Layout: hero ring with an explicit coverage line, the full breakdown sorted
by drag (each contributor showing its earned/possible points as a bar plus
its own explanation), what wasn't measured, a 7/30/90-day trend chart, and
an explainer pointing at docs/project/readiness.md.

Two deliberate choices about honesty:

- Coverage is stated on the hero whenever it is below 100%. A 74 from a
  partial night is not the same claim as a 74 from a complete one, and
  showing only the number would quietly equate them.
- Absent signals are named, not omitted. "Your temperature was fine" and
  "your temperature wasn't measured" are different statements; a
  "Not measured last night" section says which one applies, with a line
  explaining they are left out of the score rather than counted as zero.

The trend chart is the first chart in this app to be accessible to
VoiceOver. It ships an AXChartDescriptor plus per-bar labels, so the rotor
can step through days and hear "24 July, 91, Primed" instead of just
"chart". Charts.swift, VitalsCharts.swift and ActivityCharts.swift are all
still opaque; this is the pattern to back-port.

Hardening that path found a real crash. The axis description closure is
called by the framework with values the app doesn't control, and Int(Double)
traps on infinity and NaN - so an unguarded conversion took the whole app
down, and only ever for VoiceOver users. Now guarded and clamped, with a
regression test that feeds it infinity, NaN and out-of-range values.

missingKinds moved from the view onto ReadinessSnapshot: it is not
presentation logic, it is a fact about the score, and PR 4's coach tool
needs the same answer.

Also adds an -openReadiness launch arg, matching the existing test tooling.

12 new tests. 938 total, 0 failures. Verified rendering in the simulator
against seeded demo data.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>