ui: follow-ups for the panel shell, popup and accessibility #370

Items still open from the audit issue #353. The fixed items landed in #364; this issue tracks what is left. Each item says why it was not part of that fix.

From #353 (panel shell, popup and accessibility)

Open:

• Shell improvement: programmatic buildReport(): New public package API. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483)
• Shell improvement: remember scroll/selection per tab: Touches every page's state; not small or local. (done in feat(ui): remember scroll, treegrid routes, shared states, sortable tables #490)
• Shell improvement: minimized pill launcher with counts: New UI feature that needs a design decision. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483)
• Panel: Search fields differ from page to page (Low): Needs a new shared component across six or more pages and a choice between 'Filter' and 'Find'. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483)
• Panel: Route tree has no tree semantics (Low): A treegrid with expand/collapse keys is a larger restructure of route-current.ts. (done in feat(ui): remember scroll, treegrid routes, shared states, sortable tables #490)
• Panel: Filtered lists tracked by $index (Low): The listed rows have no selection and, except forms-report, no focusable content. cd-recording uses $index on purpose for repeated names (duplicate-track-keys test). No unique stable key exists without adding a keying helper. (decided: not a bug)
• Panel: Hex colors in the Analog view (Low): Moving about ten colour pairs into the palette and the contrast test is a palette change across several files, not a small fix. (done in fix: finish small follow-ups across forms, router, http, analog, signals and compat #418)
• Panel improvement: shared <app-state> component and spec: Cross-page refactor. (done in feat(ui): remember scroll, treegrid routes, shared states, sortable tables #490)
• Panel improvement: spec checking search-field/roving usage: Depends on the search-field component, which was skipped. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483 and fix: pre-release cleanup of review findings and tracker leftovers #494)
• Panel improvement: resizable panes with splitter: New feature across several pages; needs a design decision. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483)
• Panel improvement: pause live updates / auto-scroll toggles: New feature across three pages; needs a product decision. (done in feat(ui): remember scroll, treegrid routes, shared states, sortable tables #490)
• Panel improvement: sortable column headers with aria-sort: New feature across two tables; needs a design decision. (done in feat(ui): remember scroll, treegrid routes, shared states, sortable tables #490)
• Panel improvement: saved filter chips per view: New feature; needs a product decision. (done in feat(ui): Filter field, splitters, counts pill, buildReport() and extension popup and sidebar #483)
• Panel improvement: run test:axe on loading/error/no-match states: Changes the static report build and the axe harness; not local. (done in fix: work through the follow-up lists and mask Signal Forms secrets in signal graphs #438)

Tracked elsewhere

These items from the audit are not listed above because another issue already tracks them:

• A Settings view: phase 3 of 4: a shell you live in #342 (settings page)
• Shortcuts to switch tabs and focus search: phase 3 of 4: a shell you live in #342 (command palette)