fix: screenshare dismiss, GIF header, PiP resize, call subtitle, CSS vars

- CallControls: screenshare confirm now closes on Escape or click-outside
  (transparent fixed backdrop + window keydown listener); cleaned indentation
- GifPicker: TDS header rendered a JSX comment ({/* GIF_SEARCH */}) so the
  // GIF_SEARCH label was invisible; changed to {'// GIF_SEARCH'}
- CallEmbedProvider: PiP resize clamping now works at initial bottom/right
  position by normalising to top/left before parsing el.style.left
- CallEmbedProvider: incoming call subtitle now reads 'Incoming Video Call'
  or 'Incoming Voice Call' based on m.call.intent
- PollContent: progress bar background now uses --bg-surface-active /
  --bg-surface-low instead of hardcoded white (invisible in light mode)
- index.css + lotus-terminal.css.ts: define --bg-surface, --bg-surface-low,
  --bg-surface-active, --bg-surface-border, --text-primary as global CSS vars
  with vanilla fallbacks and TDS dark/light overrides; these were used by
  poll, location map, upload card and GIF picker but never defined

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

src/app/components/message/content/PollContent.tsx

@@ -280,7 +280,9 @@ export function PollContent({
                     position: 'absolute',
                     inset: 0,
                     width: `${pct}%`,
-                    background: selected ? 'rgba(255,255,255,0.10)' : 'rgba(255,255,255,0.05)',
+                    background: selected
+                      ? 'var(--bg-surface-active)'
+                      : 'var(--bg-surface-low)',
                     borderRadius: '8px',
                     pointerEvents: 'none',
                   }}