Migrate website to Starlight with full-text resource search (#883)

* Add search functionality to Learning Hub index page

Add a client-side search bar that filters articles by title, description,
and tags. Sections with no matching results are hidden automatically.
Uses the existing .search-bar CSS pattern from the cookbook page.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* chore: remove deprecated layouts, theme script, and learning-hub config

Phase 5 cleanup of Starlight migration:
- Delete BaseLayout.astro (replaced by StarlightPage)
- Delete ArticleLayout.astro (replaced by Starlight docs rendering)
- Delete theme.ts (Starlight has built-in theme toggle)
- Delete src/config/learning-hub.ts (sidebar order now in astro.config.mjs)
- Replace learning-hub glob collection with Starlight docs collection in content.config.ts
- Keep search.ts (still used by homepage and all resource page scripts)

Build verified: 23 pages, no errors.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Migrate website to Starlight with full-text resource search

- Replace bespoke Astro layouts with Starlight integration
  - Homepage and resource pages use StarlightPage wrapper
  - Learning Hub articles rendered via Starlight docs collection
  - Starlight provides search, theme toggle, sidebar, ToC, a11y

- Add custom Pagefind integration for resource search
  - All 614 agents/skills/instructions/hooks/workflows/plugins
    indexed as custom records with deep-link URLs
  - Type filter pills (horizontal pill toggles) above results
  - Search results link directly to resource modals via #file= hash

- Move global.css to src/styles/ for Vite processing
  - Scope CSS reset to #main-content to avoid Starlight conflicts
  - Full-width page gradient via body:has(#main-content)
  - Light/dark theme support with Starlight gray scale inversion

- Delete old layouts (BaseLayout, ArticleLayout), theme.ts, config

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Address PR review feedback

- Fix pagefind-resources.ts header comment (pagefind:true not false)
- Remove unused base variable in cookbook/index.astro
- Replace hardcoded /awesome-copilot/ paths with relative links in index.md
- Delete stale public/styles/global.css (source of truth is src/styles/)
- Replace fragile getBasePath() with Astro config base in pagefind integration
- Document pagefind:true reasoning in astro.config.mjs
- Use proper visually-hidden pattern + :focus-visible ring for filter pills
- Remove dead header/nav/theme CSS from global.css (~160 lines)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

website/src/integrations/pagefind-resources.ts

@@ -0,0 +1,142 @@
+/**
+ * Custom Pagefind integration that extends Starlight's search index
+ * with resource records (agents, skills, instructions, hooks, workflows, plugins).
+ *
+ * Starlight's pagefind is enabled (pagefind: true) so the search UI renders,
+ * but this integration runs AFTER Starlight's and overwrites the index with
+ * HTML pages + custom resource records combined.
+ */
+import type { AstroIntegration } from "astro";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+import * as pagefind from "pagefind";
+
+interface SearchRecord {
+  type: string;
+  id: string;
+  title: string;
+  description: string;
+  path: string;
+  tags?: string[];
+  searchText: string;
+}
+
+const TYPE_LABELS: Record<string, string> = {
+  agent: "Agent",
+  instruction: "Instruction",
+  skill: "Skill",
+  hook: "Hook",
+  workflow: "Workflow",
+  plugin: "Plugin",
+  tool: "Tool",
+};
+
+const TYPE_PAGES: Record<string, string> = {
+  agent: "/agents/",
+  instruction: "/instructions/",
+  skill: "/skills/",
+  hook: "/hooks/",
+  workflow: "/workflows/",
+  plugin: "/plugins/",
+  tool: "/tools/",
+};
+
+export default function pagefindResources(): AstroIntegration {
+  let siteBase = "/";
+
+  return {
+    name: "pagefind-resources",
+    hooks: {
+      "astro:config:done": ({ config }) => {
+        siteBase = config.base;
+      },
+      "astro:build:done": async ({ dir, logger }) => {
+        const log = logger.fork("pagefind-resources");
+        const now = performance.now();
+
+        try {
+          log.info("Building search index with Pagefind + resource records...");
+
+          const response = await pagefind.createIndex();
+          if (response.errors.length > 0) {
+            for (const err of response.errors) log.error(err);
+            throw new Error("Failed to create Pagefind index");
+          }
+          const { index } = response;
+
+          // Index all built HTML pages (same as Starlight's default)
+          const indexResult = await index.addDirectory({
+            path: fileURLToPath(dir),
+          });
+          if (indexResult.errors.length > 0) {
+            for (const err of indexResult.errors) log.error(err);
+            throw new Error("Failed to index HTML directory");
+          }
+          log.info(`Indexed ${indexResult.page_count} HTML pages.`);
+
+          // Read and index resource records from search-index.json
+          const searchIndexPath = fileURLToPath(
+            new URL("./data/search-index.json", dir)
+          );
+          let records: SearchRecord[];
+          try {
+            records = JSON.parse(readFileSync(searchIndexPath, "utf-8"));
+          } catch {
+            log.warn("Could not read search-index.json, skipping resource indexing.");
+            records = [];
+          }
+
+          // Use the base path from Astro config (e.g. "/awesome-copilot/")
+          const base = siteBase.endsWith("/") ? siteBase : `${siteBase}/`;
+
+          let added = 0;
+          for (const record of records) {
+            const typePage = TYPE_PAGES[record.type];
+            if (!typePage) continue;
+
+            const url = `${base}${typePage.slice(1)}#file=${encodeURIComponent(record.path)}`;
+            const typeLabel = TYPE_LABELS[record.type] || record.type;
+
+            const addResult = await index.addCustomRecord({
+              url,
+              content: record.searchText || `${record.title} ${record.description}`,
+              language: "en",
+              meta: {
+                title: `${record.title} — ${typeLabel}`,
+              },
+              filters: {
+                type: [record.type],
+              },
+            });
+
+            if (addResult.errors.length > 0) {
+              for (const err of addResult.errors) log.warn(`Record ${record.id}: ${err}`);
+            } else {
+              added++;
+            }
+          }
+
+          log.info(`Added ${added} resource records.`);
+
+          // Write the combined index
+          const writeResult = await index.writeFiles({
+            outputPath: fileURLToPath(new URL("./pagefind/", dir)),
+          });
+          if (writeResult.errors.length > 0) {
+            for (const err of writeResult.errors) log.error(err);
+            throw new Error("Failed to write Pagefind files");
+          }
+
+          const elapsed = performance.now() - now;
+          log.info(
+            `Search index built in ${elapsed < 750 ? `${Math.round(elapsed)}ms` : `${(elapsed / 1000).toFixed(2)}s`}.`
+          );
+        } catch (cause) {
+          throw new Error("Failed to build Pagefind search index.", { cause });
+        } finally {
+          await pagefind.close();
+        }
+      },
+    },
+  };
+}