feat: add toggleable hotkey hints to sidebar buttons and refac ShortcutsModal

- Add src/lib/shortcuts.ts as the single source of truth for every shortcut
- Create HotkeyHint.svelte to show OS-aware key combos (⌘ on Mac, Ctrl elsewhere)
- Make sidebar “New Chat” and “Search” buttons display their shortcuts on hover
- Add user setting to toggle these sidebar hints
- Refactor ShortcutsModal into categorized (Global, Chat, Message, Input), data-driven sections
- Introduce ShortcutItem.svelte to render each row, dividers, and multi-line text
- Fix “Focus text area” action and include “Close modal” shortcut
- Wire everything through +layout.svelte and the shortcuts registry

src/lib/components/chat/ShortcutItem.svelte

@@ -0,0 +1,58 @@
+<script lang="ts">
+	import { getContext } from 'svelte';
+	import Tooltip from '../common/Tooltip.svelte';
+	import type { Shortcut } from '$lib/shortcuts';
+
+	export let shortcut: Shortcut;
+	export let isMac: boolean;
+
+	const i18n = getContext('i18n');
+
+	function formatKey(key: string): string {
+		const lowerKey = key.toLowerCase();
+
+		if (lowerKey === 'mod') return isMac ? '⌘' : 'Ctrl/⌘';
+		if (lowerKey === 'shift') return isMac ? '⇧' : 'Shift';
+		if (lowerKey === 'backspace') return '⌫/Delete';
+		if (lowerKey === 'escape') return 'Esc';
+		if (lowerKey === 'enter') return 'Enter';
+		if (lowerKey === 'tab') return 'Tab';
+		if (lowerKey === 'arrowup') return '↑';
+		if (lowerKey === 'arrowdown') return '↓';
+
+		// For keys like 'KeyK', 'KeyO', etc., we just want the last character.
+		if (lowerKey.startsWith('key')) return key.slice(-1);
+		// For keys like 'Digit2', 'Digit3', etc.
+		if (lowerKey.startsWith('digit')) return key.slice(-1);
+		// For other special keys
+		if (lowerKey === 'quote') return "'";
+		if (lowerKey === 'period') return '.';
+		if (lowerKey === 'slash') return '/';
+		if (lowerKey === 'semicolon') return ';';
+
+		return key.toUpperCase();
+	}
+</script>
+
+<div class="w-full flex justify-between items-center">
+	<div class="text-sm whitespace-pre-line">
+		{#if shortcut.tooltip}
+			<Tooltip content={$i18n.t(shortcut.tooltip)}>
+				<span class="whitespace-nowrap">
+					{$i18n.t(shortcut.name)}<span class="text-xs">&nbsp;*</span>
+				</span>
+			</Tooltip>
+		{:else}
+			{$i18n.t(shortcut.name)}
+		{/if}
+	</div>
+	<div class="flex-shrink-0 flex items-center self-center space-x-1 text-xs">
+		{#each shortcut.keys as key}
+			<div
+				class="h-fit py-1 px-2 flex items-center justify-center rounded-sm border border-black/10 capitalize text-gray-600 dark:border-white/10 dark:text-gray-300"
+			>
+				{formatKey(key)}
+			</div>
+		{/each}
+	</div>
+</div>