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/index.css

@@ -9,6 +9,13 @@
 :root {
   --tc-link: hsl(213deg 100% 45%);
 
+  /* semantic surface vars used by poll, location, upload card, gif picker */
+  --bg-surface: #ffffff;
+  --bg-surface-low: rgba(0, 0, 0, 0.04);
+  --bg-surface-active: rgba(0, 0, 0, 0.10);
+  --bg-surface-border: rgba(0, 0, 0, 0.14);
+  --text-primary: #1a1a1a;
+
   /* user mxid colors */
   --mx-uc-1: hsl(208, 100%, 45%);
   --mx-uc-2: hsl(302, 100%, 30%);
@@ -27,6 +34,13 @@
 .butter-theme {
   --tc-link: hsl(213deg 100% 80%);
 
+  /* semantic surface vars — dark overrides */
+  --bg-surface: #25272e;
+  --bg-surface-low: rgba(255, 255, 255, 0.05);
+  --bg-surface-active: rgba(255, 255, 255, 0.10);
+  --bg-surface-border: rgba(255, 255, 255, 0.12);
+  --text-primary: #e0e5ed;
+
   --mx-uc-1: hsl(208, 100%, 75%);
   --mx-uc-2: hsl(301, 100%, 80%);
   --mx-uc-3: hsl(163, 100%, 70%);