feat(a11y,perf): comprehensive icon button labels, toolbar a11y, timeline binary search

A11y C-1: aria-label on 30+ remaining icon-only buttons across:
  - settings panels (close, reset, info, expand, remove, undo)
  - editor toolbar (bold, italic, underline, strike, code, spoiler,
    blockquote, code block, ordered/unordered list, headings 1-3)
  - auth stages (cancel buttons in SSO, Password stages)
  - device verification (cancel buttons)
  - password input (show/hide toggle with dynamic label)
  - event readers, account data editor close buttons
  - global emoji packs (add/remove buttons)
Perf-5: Replace O(N×T) getTimelineAndBaseIndex scan with precomputed binary
  search (timelineSegments useMemo) — O(log T) per visible message render

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/components/password-input/PasswordInput.tsx

@@ -28,6 +28,7 @@ export const PasswordInput = forwardRef<HTMLInputElement, PasswordInputProps>(
                   variant={visible ? 'Warning' : variant}
                   size="300"
                   radii="300"
+                  aria-label={visible ? 'Hide password' : 'Show password'}
                 >
                   <Icon
                     style={{ opacity: config.opacity.P300 }}