feat(inline-edit): add WYSIWYG inline dashboard editing mode

Replace the disconnected board edit page with inline editing directly
on the board view. Toggle with Ctrl+E or the Edit button. Features:

- Edit mode store with changeset accumulation and batch save
- Floating toolbar (save, discard, add section, board settings, exit)
- Widget hover overlays with edit/delete/drag controls
- Type-specific widget config panels for all 14 widget types
- Section inline editing (title, icon picker, delete)
- "+" buttons for adding widgets and sections inline
- Section-level drag-and-drop reordering via svelte-dnd-action
- Batch save API endpoint (single Prisma transaction)
- Board properties side panel with live theme/wallpaper preview
- Modal widget type picker with search filtering
- Icon picker component with visual grid and search
- Confirmation dialog modal for all destructive actions
- HTML format support for Note widget (in addition to markdown/text)
- Full i18n support (en + ru) for all new UI strings
- Legacy edit page banner linking to new inline mode

src/routes/boards/[boardId]/edit/+page.svelte

@@ -186,8 +186,25 @@
 			</div>
 		{/if}
 
+		<!-- Inline edit mode banner -->
+		<div class="mb-4 flex items-center gap-3 rounded-xl border border-primary/30 bg-primary/5 p-4">
+			<svg xmlns="http://www.w3.org/2000/svg" width="20" height="20" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="shrink-0 text-primary">
+				<path d="M17 3a2.85 2.83 0 1 1 4 4L7.5 20.5 2 22l1.5-5.5Z" /><path d="m15 5 4 4" />
+			</svg>
+			<div class="flex-1">
+				<p class="text-sm font-medium text-foreground">{$t('board.try_inline_edit') ?? 'Try the new inline edit mode!'}</p>
+				<p class="text-xs text-muted-foreground">{$t('board.inline_edit_description') ?? 'Edit your board directly with live preview. Press Ctrl+E on the board page.'}</p>
+			</div>
+			<a
+				href="/boards/{data.board.id}?edit=true"
+				class="shrink-0 rounded-lg bg-primary px-3 py-1.5 text-sm font-medium text-primary-foreground transition-colors hover:bg-primary/90"
+			>
+				{$t('board.open_inline_edit') ?? 'Open Inline Edit'}
+			</a>
+		</div>
+
 		<div class="mb-6 flex items-center justify-between">
-			<h1 class="text-2xl font-bold text-foreground">{$t('board.edit_board')}</h1>
+			<h1 class="text-2xl font-bold text-foreground">{$t('board.edit_board')} <span class="text-sm font-normal text-muted-foreground">({$t('board.advanced') ?? 'Advanced'})</span></h1>
 			<a
 				href="/boards/{data.board.id}"
 				class="rounded-lg border border-border px-4 py-2 text-sm text-foreground transition-colors hover:bg-accent"