Make dashboard readable at maximum accessibility text

[FZ2000]

Effect in one sentence

Makes the hardened Dashboard readable at very large and maximum accessibility text, including retained-error states, without changing its normal-size hierarchy or data contract.

Stack position

6 of 6: #153 → #155 → #157 → #159 → #160 → #161 (this accessibility follow-up).

This branch is based on current #160 head fbd6c69, not main. The stack is an alternative to standalone #152.

Central behavior

• Dashboard-local semantic font roles read the injected DynamicTypeSize directly and apply explicit macOS scaling. This replaces the ineffective @ScaledMetric assumption found during native-host testing.
• xLarge remains the last compact two-column/table state. At .xxLarge and above, the brief, signal rail, Recent Work, card headers, and usage history reflow before fixed geometry becomes unsafe.
• Recent Work replaces fixed columns with complete vertical rows. Maximum-size usage history becomes a date/value list rather than a compressed chart; static facts are not exposed as controls.
• Global refresh/list errors participate in the scroll document instead of overlaying and obscuring final rows at maximum text size.
• Full-content snapshot configurations measure the intrinsic Dashboard before capture and fail if the requested canvas would clip it.
• Normal-size views retain the compact two-column hierarchy and chart; their existing canonical references are byte-preserved against Make dashboard honest across real-world states #160.

Review order

1. DashboardFontRole, DashboardFontModifier, and dashboardUsesAccessibilityLayout in DashboardPane.swift.
2. Large-text branches for the brief, proof facts, signals, Recent Work, usage history, and in-flow error alert.
3. Intrinsic measurement and clipping rejection in DashboardSnapshotHarness.swift.
4. Boundary/native-host tests and the five new canonical references: xLarge, xxLarge, accessibility5 light/dark, and accessibility5 retained-error.

Verification at current head 70acf39

• Full Python suite on the inherited final Python tree: 2,652 passed, 1 external Starlette deprecation warning.
• swift test: 155 executed, 5 expected opt-in visual skips, 0 failures.
• DashboardInteractionTests: 51 passed, including native-host font growth and the xLarge/xxLarge transition.
• DashboardSnapshotHarnessTests: 10 passed, including full-content clipping rejection and maximum-text retained-error coverage.
• ./Scripts/visual-snapshots verify: About, Dashboard, Menu, Usage, and Work all match the pinned canonical renderer.
• All 13 Dashboard references match. The five new images were manually inspected; the largest retained-error artifact is 1920×5800 and shows every work and usage row without occlusion or excessive dead space.
• swift build -c release: passed.
• Effective diff against Make dashboard honest across real-world states #160: 11 Dashboard-only files; git diff --check is clean.
• Two independent final code/scenario audits: GO, no remaining blocker.

Current-head GitHub CI: Python 3.11/3.12/3.13 and macOS app/snapshot jobs all passed.

Scope and validation boundary

This PR is intentionally Dashboard-local. Data truth, pagination, retained-error, and request-race behavior live in #160. Shared top-bar typography remains compact and fully visible at the supported 960-point minimum, but app-wide typography migration is not part of this change.

Canonical snapshots and native-host measurements prove deterministic geometry and font growth; they do not substitute for a live manual VoiceOver traversal or keyboard-focus smoke. No PR in this stack is merged by this change.