Implement stat block panel fold/unfold and pin-to-second-panel

Replace the close button and heading with fold/unfold controls that
collapse the panel to a slim right-edge tab showing the creature name
vertically, and add a pin button (xl+ viewports with creature loaded)
that opens the creature in a second left-side panel for simultaneous
reference. Fold state is respected on turn change. 19 acceptance tests.

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

apps/web/src/index.css

@@ -84,6 +84,14 @@
 	animation: confirm-pulse 300ms ease-out;
 }
 
+@utility transition-slide-panel {
+	transition: translate 200ms ease-out;
+}
+
+@utility writing-vertical-rl {
+	writing-mode: vertical-rl;
+}
+
 @utility animate-concentration-pulse {
 	animation:
 		concentration-shake 450ms ease-out,