v0.20.0 — accessibility & quality audit

A full Front-End Checklist audit of every component (#139,
DS-0161): 58 findings in 30 components, all fixed. Several fixes change default behaviour; those
are listed first.

Changed

• BREAKING — MetricTile (DS-0191) is no longer a live region by default. Pass the new
  live prop to announce updates; the whole tile is then one polite, atomic region, so an update
  reads as "label value delta" rather than a bare number.
• BREAKING — ServiceCard (DS-0192) is interactive only with href or onclick; without
  them it is a static group, not a focusable button. spark defaults to [] (shows "No data"
  rather than a made-up trend). The control is a stretched overlay named by name + status and
  described by host, latency, meta and the sparkline.
• BREAKING — Card (DS-0183) with onclick renders a stretched overlay <button>; the root
  is no longer role="button", so nested actions are no longer inside a button. A titled card is
  role="region".
• Table (DS-0188) renders data-align="start" | "end" (was left / right); align
  accepts start / end and still takes left / right. Alignment follows text direction.
• Sidebar (DS-0181): the rail toggle is named "Sidebar" with aria-expanded (was
  "Expand / Collapse sidebar" with aria-pressed). Degraded and down status is spoken, not
  colour-only. Ids are unique per instance.
• FileDrop (DS-0173) is named by its visible text ("Drop files here"), not "Upload files".
• Toaster (DS-0179): side positions anchor to the inline edge, so top-right renders top
  left under dir="rtl".
• Modal (DS-0178): the header snippet receives titleId (Snippet<[string]>), so a
  custom header keeps the dialog named. Snippets that ignore the argument keep working.

Added

• Chart keyboard contract (src/lib/chart-nav.ts): Chart, BoxPlot, BumpChart,
  ScatterPlot and Heatmap are each one tab stop; arrows, Home and End move between marks.
• Chart (DS-0184): dashes (default on) tells line and area series apart by dash pattern
  as well as colour, with matching legend keys; endLabels prints each series name at the end of
  its line. CHART_DASH_CYCLE is exported.
• Heatmap (DS-0164): a min→max legend when showValues is off.
• FileDrop: onreject(files), and rejected files are announced.
• SearchPalette (DS-0180): closeLabel and resultsText; a visible close button below
  768px and an announced result count.
• lockScroll / unlockScroll exported from dssoca/vanilla.js: the reference-counted page
  scroll lock that Modal and SearchPalette share.
• MetricTile: live.

Fixed

• Focus rings — Switch, Input (clear button), NumberField (steppers), SegmentedControl,
  Table (sort button), Menu (trigger) and Pagination replaced the base ring with a
  --ss-primary-soft glow at about 1.5:1. They now show a solid --ss-primary ring.
• Accordion (DS-0162): collapsed panels are inert and visibility: hidden; their content
  no longer stays in the tab order and the accessibility tree.
• Tooltip (DS-0163): aria-describedby goes on the focused trigger, not a wrapper that
  never takes focus. Escape closes the tip from anywhere and the pointer can move onto it.
• Heatmap: value text stays legible on every cell strength (was about 1.1:1 on strong cells).
• Charts: data marks are role="img" (Heatmap: gridcell), not buttons that do nothing;
  tooltips are hidden from assistive tech and close on Escape; BoxPlot labels include min / max.
• NumberField (DS-0168): steppers are aria-disabled at the bounds, so focus no longer
  drops to <body>; the value is announced.
• FileDrop: focus moves to a neighbour after Remove and Clear; 24px targets.
• Toaster: persistent polite and assertive live regions; focus is restored when a focused
  toast is dismissed; the timer does not resume while a toast has focus; 24px dismiss target.
• Link (DS-0174): inline links show an underline at rest; noopener noreferrer and the
  new-tab hint follow the real target; a custom rel is merged.
• Badge (DS-0175): a count-only badge is named by its count; a nameless dot is not img.
• Menu (DS-0177): without label, the menu is named by its trigger.
• Modal / SearchPalette: the page behind no longer scrolls.
• Topbar (DS-0182): the tab strip stays reachable when active matches no tab.
• LogStream (DS-0190): switched-off chips keep AA contrast; the log scroller is focusable;
  the empty state is no longer a nested live region.
• Icon (DS-0176): paths and registerIcon markup passes a defence-in-depth filter; the
  trust requirement is documented.
• Button (DS-0165): warns when iconOnly has no accessible name.
• TierList (DS-0189): the flip animation respects reduced motion; arrow keys and drag
  insertion mirror under RTL.
• RTL — logical properties replace physical left / right in Input, Textarea,
  NumberField, DateField, Select, Switch, SegmentedControl, Table, Menu, Sidebar,
  Pagination, SearchPalette, Toaster, Topbar and ShortcutsHelp; SegmentedControl arrow
  keys follow reading direction.

Docs

• CLAUDE.md gains Accessibility & quality rules for every component change (DS-0194), and
  test/unit/checklist-guards.test.ts enforces the mechanical ones across all components.
• Inspirations (DS-0195): the twelve example pages and the gallery follow the new component
  markup and had a polish pass (quiet chrome, accent only where it matters, fewer badges).