UI iteration 4: dock morph animation, sticky-in-flow dock, scrollbar, indicators

- Animation: the blob's shell morphs height (WAAPI, 180ms) on every
  variant change — chat ↔ question ↔ collapsed bar — plus a quick
  fade/rise (160ms) on the swapped content. Gotcha pinned in code: never
  measure the shell while a morph is in flight (getBoundingClientRect
  reads the ANIMATED value and corrupts the next morph's start height);
  cancel running morphs before measuring, refresh settled height only
  when no morph is running.
- Gradient-over-scrollbar fixed structurally: the dock is no longer an
  absolute overlay on the conversation root — it's sticky bottom-0 INSIDE
  the scroller (in flow). The transcript scrolls fully clear of the dock,
  the fade never touches the scrollbar lane, and the pb-hack clearances
  are gone.
- New question while at the bottom scrolls to reveal the dock; scrolled
  up → collapsed bar, no yank.
- Thin dark native scrollbar app-wide (8px webkit + scrollbar-width:thin,
  dark thumb, transparent track). Note: use-stick-to-bottom sets
  scrollbar-gutter: stable both-edges on its scroller — the lane is
  outside the content flow by design.
- 'Writing a question…' transcript shimmer while a tool call streams its
  input (same slot as 'Thinking…'). Protocol pinned by a test asserting
  tool-input-start precedes tool-input-available; scripted mock now
  streams tool input as deltas like real providers do. (OpenRouter/
  Anthropic often delivers the whole input in ONE delta — then the dock
  appears instantly and no indicator is needed or shown.)

Verified live: grow 54→349px and shrink 349→54px fire with correct
from/to; collapse/expand intact; gradient stops before the gutter;
Thinking… observed in-page; 58/58 tests.

app/globals.css

@@ -84,3 +84,46 @@ body {
 	background: var(--color-background);
 	color: var(--color-foreground);
 }
+
+/* Thin dark native scrollbar (app-wide): dark thumb, transparent track. */
+* {
+	scrollbar-width: thin;
+	scrollbar-color: var(--color-border) transparent;
+}
+
+::-webkit-scrollbar {
+	width: 8px;
+	height: 8px;
+}
+
+::-webkit-scrollbar-track {
+	background: transparent;
+}
+
+::-webkit-scrollbar-thumb {
+	background: var(--color-border);
+	border-radius: 8px;
+}
+
+::-webkit-scrollbar-thumb:hover {
+	background: var(--color-muted-foreground);
+}
+
+/* Dock variant swap — quick fade/rise on content change; the shell's HEIGHT
+   morph is separate (WAAPI in DockOverlay). Re-applied via class toggling, no
+   remount, so collapsed-question state survives. */
+@keyframes dock-variant-in {
+	from {
+		opacity: 0;
+		transform: translateY(6px);
+	}
+
+	to {
+		opacity: 1;
+		transform: translateY(0);
+	}
+}
+
+.dock-variant {
+	animation: dock-variant-in 160ms cubic-bezier(0.2, 0.8, 0.2, 1);
+}