Fix Archive toolbar and header geometry on mobile

[Chris0Jeky]

Summary

• Stack the Archive header toggle and filter/refresh controls at phone widths while preserving desktop row flow.
• Constrain long labels, keep the existing four board actions in their shipped two-column mobile layout, and provide a visible scoped focus ring.
• Add a browser geometry regression covering synthetic long localized labels at 375px and 390px, desktop flow, viewport containment, no horizontal overflow, focus, and action order.

Refs #2075

Verification

• Baseline detector failed before the CSS change: at 375px the header toggle remained on the heading row.
• npx vitest --run --maxWorkers=2 "src/tests/views/ArchiveView.spec.ts" — 9 passed.
• npm run typecheck — passed.
• npm run build — passed; existing ineffective dynamic-import warning only.
• Scoped ESLint and git diff --check — passed.
• Full mobile-responsive.spec.ts — 16 passed across mobile Chromium and Safari with the repository-supported Mock LLM environment.

Hosted CI/review remains to be observed on the open PR.

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[Chris0Jeky]

Fresh-context review record (coordinator, 2026-09-06; read-only Opus 5 reviewer over the diff against the merge base; route: the standing D-12 rule for Codex-session PRs — review, fix MEDIUM+ in-PR, merge, disposition comment).

VERDICT: SHIP (round 1). Fixed in-PR (round 2, coordinator commit ccd5b3602): MEDIUM-1 — the align-items: center on the toolbar and the flex: 1 1 12rem; min-width: 0 on the input sat outside the max-width: 640px block, so desktop changed (the select grew to fill the toolbar, Refresh stopped matching its height) while the body and the file comment said desktop was unchanged; both are now mobile-only (min-width: 0 moved into the media block). MEDIUM-3 — the stacked input and Refresh had no 44 px floor unlike the sibling actions rule; added. Not run locally (e2e needs a stack); the hosted E2E Smoke run at the new head proves it.

Tracked for #2075, not fixed: MEDIUM-2 — the focus-ring assertion (outlineStyle !== 'none' || boxShadow !== 'none') passes on the pre-fix tree because the global *:focus-visible rules already apply, so the "visible scoped focus ring" bullet is unproven and the new :deep(.pbtn:focus-visible) rule is largely redundant. LOWs: the test registers a second user and a second init script on top of beforeEach; legacy-theme only while Paper is the default; toHaveLength(7) and the .paper-archive__row wait may race boards-still-loading.