refactor: migrate icon rendering to SVG sprite pattern

Replace per-icon inline SVG rendering with a centralized sprite system. Icons are now collected once per page and rendered as <symbol> elements, referenced via <use> tags. Eliminates redundant icon fetching, reduces HTML size, and simplifies icon management across components.

web/src/routes/admin/projects/[id]/+page.server.ts

@@ -1,22 +1,31 @@
 import type { PageServerLoad } from "./$types";
 import { apiFetch } from "$lib/api.server";
-import { addIconsToTags } from "$lib/server/tag-icons";
-import type { AdminProject, AdminTagWithCount } from "$lib/admin-types";
+import { collectTagIcons } from "$lib/server/tag-icons";
+import type {
+  AdminProject,
+  AdminTagWithCount,
+  AdminTag,
+} from "$lib/admin-types";
 
 export const load: PageServerLoad = async ({ params, fetch }) => {
   const { id } = params;
 
   // Fetch project and tags in parallel
-  const [project, tagsWithCounts] = await Promise.all([
+  const [project, availableTags] = await Promise.all([
     apiFetch<AdminProject>(`/api/projects/${id}`, { fetch }).catch(() => null),
     apiFetch<AdminTagWithCount[]>("/api/tags", { fetch }),
   ]);
 
-  // Add icons to tags
-  const availableTags = await addIconsToTags(tagsWithCounts);
+  // Collect icons for sprite (from available tags + project tags)
+  const allTags: AdminTag[] = [...availableTags];
+  if (project) {
+    allTags.push(...project.tags);
+  }
+  const icons = await collectTagIcons(allTags);
 
   return {
     project,
     availableTags,
+    icons,
   };
 };