feat(frontend): open bottom panel at full height (80vh) by default

Panel now opens to 80 % of the viewport height so the user can immediately
read comments and metadata without having to drag it up first.
The user can drag the top handle down to make it smaller; that size is
persisted to localStorage and restored on the next visit.

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

frontend/src/lib/components/DocumentBottomPanel.svelte

@@ -68,7 +68,6 @@ let {
 }: Props = $props();
 
 const MIN_HEIGHT = 52; // drag handle (8px) + tab bar (~44px)
-const DEFAULT_HEIGHT = 320;
 
 let isDragging = $state(false);
 let dragStartY = 0;
@@ -78,7 +77,7 @@ function openTab(tab: Tab) {
 	activeTab = tab;
 	if (!open) {
 		open = true;
-		if (height <= MIN_HEIGHT) height = DEFAULT_HEIGHT;
+		if (height <= MIN_HEIGHT) height = Math.floor(window.innerHeight * 0.8);
 	}
 }
 
@@ -104,7 +103,7 @@ function onDragMove(e: PointerEvent) {
 		open = false;
 	} else {
 		open = true;
-		height = Math.max(DEFAULT_HEIGHT / 4, Math.min(newHeight, maxHeight));
+		height = Math.max(80, Math.min(newHeight, maxHeight));
 	}
 }