[Frontend][Paper] Card inspector follow-ups from the #2097/#2100 review rounds (P2 batch)

[Chris0Jeky]

Unaddressed Codex P2s from merged PRs #2097/#2100, batched (2026-08-26 sweep):

1. Desktop @media(min-width:768px) .card-modal-viewport rule (equal specificity) overrides inspector top/height with inset:0/height:auto.
2. Density control in the non-wrapping flex:none action row overflows a 390px viewport, pushing header controls off-screen.
3. After a confirmed A->B card switch, CardModal keeps card A as previouslyFocusedElement; closing B returns focus to A (possibly off-screen).
4. On desktop-inspector -> modal transition (resize/orientation), the isOpen watcher does not rerun: focus stays behind the overlay, Tab trap not engaged.
5. Fire-and-forget fetchCardComments has no rejection handler -> unhandled rejection on failed loads.
6. beforeunload is registered for the whole Paper board visit, not only while dirty -> disables Firefox bfcache on clean boards (full reload).

Refs #2097 #2100.

[Chris0Jeky]

Coordinator disposition (2026-09-06, Codex-session PR carried under the standing D-12 route: fresh-context review, MEDIUM+ fixed in-PR, merged as a merge commit).

PR #2735 (Handle card comment load rejection) merged as 881c560dd; review SHIP, MEDIUM-1 fixed in-PR (the swallowed rejection is now logErrored, the only reporting sink once caught). Remaining: LOW (pre-existing) — a rejected load renders "No comments yet." in CardModalComments.vue, the honest-empty lie class; the "stale rejection" test's assertions also pass on base; a now-false ordering comment in useCardModal.spec.ts.