Add landing page (web/) with Next.js + Tailwind

- Minimal centered layout with Geist sans font
- Typing animation cycling through agent names
- Light/dark mode toggle via next-themes
- Download for Mac button linking to latest DMG
- Feature list, GitHub + Docs footer links
- Meta tags and Open Graph for SEO
- CI: add web typecheck job (tsc --noEmit)

.github/workflows/ci.yml

@@ -7,6 +7,26 @@ on:
   pull_request:
 
 jobs:
+  web-typecheck:
+    runs-on: ubuntu-latest
+    defaults:
+      run:
+        working-directory: web
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+
+      - name: Install dependencies
+        run: npm ci
+
+      - name: Typecheck
+        run: npx tsc --noEmit
+
   ui-tests:
     runs-on: self-hosted
     concurrency: