fix: checklist UX polish — spacing, disable markdown toggle, default to raw mode

- Increase gap between checkbox and text input (gap-1 → gap-2)
- Disable markdown toggle button in checklist mode
- Default to raw markdown mode when opening checklist notes as text

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

src/lib/components/Checklist.svelte

@@ -120,7 +120,7 @@
 		class="space-y-1"
 	>
 		{#each activeItems as item (item.id)}
-			<div class="group flex items-center gap-1" animate:flip={{ duration: flipDurationMs }}>
+			<div class="group flex items-center gap-2" animate:flip={{ duration: flipDurationMs }}>
 				<div use:dragHandle aria-label="drag handle" class="drag-handle cursor-grab opacity-0 group-hover:opacity-100 focus:opacity-100 transition-opacity duration-150" data-testid="checklist-drag-handle">
 					<GripVertical class="h-4 w-4 text-[var(--text-muted)]" />
 				</div>

src/lib/components/NoteEditor.svelte

@@ -30,7 +30,7 @@
 	// svelte-ignore state_referenced_locally
 	let checklistMode = $state(note?.checklistMode ?? false);
 	let showColorPicker = $state(false);
-	let rawMarkdownMode = $state(false);
+	let rawMarkdownMode = $state(note?.checklistMode ?? false);
 	let textareaEl: HTMLTextAreaElement | undefined = $state();
 	let tiptapEditor: Editor | undefined = $state();
 	let editorTick = $state(0);
@@ -166,8 +166,9 @@
 				<!-- Raw markdown mode toggle -->
 				<button
 					onclick={toggleMarkdownMode}
-					class="rounded-sm p-2 hover:bg-[var(--border)]/10"
+					class="rounded-sm p-2 hover:bg-[var(--border)]/10 disabled:opacity-30 disabled:cursor-not-allowed"
 					title={rawMarkdownMode ? 'Rich text mode' : 'Markdown mode'}
+					disabled={checklistMode}
 					data-testid="markdown-toggle"
 				>
 					{#if rawMarkdownMode}