feat(frontend): replace emoji with inline Material Symbols icon system

Add a self-contained icon system: vendored Material Symbols registry, an
<Icon> component that references a single <symbol> sprite via <use>, plus
IconButton/IconSprite. Replace every emoji/Unicode glyph (logo, theme
switcher, cover placeholder, like/comment counts, lightbox controls, back
links) and add leading icons to key controls. Decorative icons are
aria-hidden; icon-only buttons get labels; theme toggles expose
aria-pressed; counters get accessible names.

Recorded in openspec change material-icons-ui (all tasks complete).

frontend/src/lib/components/Comments.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { api } from '$lib/api';
+	import Icon from './Icon.svelte';
 	import { auth } from '$lib/stores/auth.svelte';
 	import type { Comment } from '$lib/types';
 
@@ -61,9 +62,14 @@
 			{#if auth.user?.id === comment.user_id}
 				<button
 					type="button"
-					class="text-text-subtle hover:text-danger text-xs"
-					onclick={() => remove(comment.id)}>удалить</button
+					class="text-text-subtle hover:text-danger inline-flex shrink-0 items-center gap-0.5 text-xs"
+					aria-label="Удалить комментарий"
+					title="Удалить комментарий"
+					onclick={() => remove(comment.id)}
 				>
+					<Icon name="delete" class="size-3.5" />
+					удалить
+				</button>
 			{/if}
 		</div>
 	{/each}
@@ -75,9 +81,13 @@
 				placeholder="Комментарий…"
 				class="border-border bg-bg text-text flex-1 rounded-lg border px-3 py-1.5 text-sm"
 			/>
-			<button class="bg-primary text-primary-fg rounded-lg px-3 py-1.5 text-sm" type="submit"
-				>Отправить</button
+			<button
+				class="bg-primary text-primary-fg inline-flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-sm"
+				type="submit"
 			>
+				<Icon name="send" class="size-4" />
+				Отправить
+			</button>
 		</form>
 	{/if}
 	{#if error}