fix(filesharing): inline cancel button, fit responsive QR to parent

[rubenhensen]

Summary

• Inline the upload cancel control inside the progress box as a small red rectangular button, matching the PostGuard style instead of the previous mismatched gradient pill.
• Make the responsive Yivi QR (YiviQRCode with responsive) scale to fit its parent (width: 100%; max-width: 330px; aspect-ratio: 1/1) so it no longer overflows the decrypt card on narrow layouts.

Test plan

• Encrypt flow: while files are uploading, the cancel button sits inside the progress box on the right; clicking it aborts and returns to file selection.
• Download page on a narrow viewport: the QR stays inside the "Decrypt with Yivi" card with no horizontal overflow.
• Download page on a wide viewport: the QR remains capped at 330px and stays square.

[rubenhensen]

/dobby review

[dobby-coder]

Reviewed the diff and the surrounding context.

SendButton.svelte — inline cancel button

• Moving the cancel control into .upload-info-content reads naturally with .upload-info-label { flex: 1 } pushing it to the right.
• Styling uses existing tokens (--pg-input-error, --pg-on-primary, --pg-font-weight-medium, --pg-border-radius-sm), so it stays consistent with PostGuard design language rather than introducing a one-off colour.
• Good a11y bits: type="button", :focus-visible outline, :disabled styling honouring encryptState.selfAborted. Translation key filesharing.cancel reused.
• all: unset is a sensible reset for a fully custom button; box-sizing: border-box is kept explicitly afterward, which is the right pattern.

YiviQRCode.svelte — responsive sizing

• width: 100%; max-width: 330px; aspect-ratio: 1/1 matches the fixed 330×330 used in the non-responsive variant, so the upper bound is unchanged.
• The existing :global(canvas), :global(svg) { width: 100% !important; height: auto !important } already handled inner sizing, so the container fix is the missing piece.

Minor (non-blocking): min-height: 200px combined with aspect-ratio: 1/1 will break the square ratio if the parent container is ever narrower than 200px (height would clamp at 200 while width drops below). The decrypt card layout in /download is unlikely to hit that on real devices, so this is just a note — no action needed.

Approving. Once arm64 build comes back green, this is good to merge.

[dobby-coder]

Dobby sees the review request, sir! Dobby will look at the cancel-button move and the responsive QR sizing and report back.

[dobby-coder]

Reviewed post-merge. Both changes look good:

• SendButton cancel button: Move from the standalone gradient pill to an inline red button inside the progress box is a clean visual fix. Uses all: unset correctly with type="button", keeps :focus-visible, :hover, and :disabled states. color-mix for the hover tint is fine — supported across all targeted browsers per the existing usage in this repo.
• YiviQRCode responsive: width: 100%; max-width: 330px; aspect-ratio: 1/1 is the right idiom for the responsive variant; preserves the 330px cap on wide layouts and stops overflow on narrow ones without needing JS sizing.

One small note (non-blocking, pure observation): --pg-input-error in dark mode is #de3030, which against white text at font-size-sm is around the 4.5:1 WCAG AA threshold for small text. Worth eyeballing in dark mode if anyone is nearby; not a regression from before, since the previous cancel button was also a colored pill.