feat: initial scaffold

- SvelteKit 2 + Svelte 5 + Tailwind 3 (JS only, paths.base=/mathmax)
- Vietnamese landing page: hero + scope (lớp 6-9) + 3 topic cards (Số học, Đại số, Hình học) all "Sắp ra mắt"
- GitHub Actions: CI (build) on PR + deploy to Pages on main
- Apache-2.0 LICENSE, README, RUNBOOK, CHANGELOG

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  pull_request:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+          # TODO: add `cache: 'npm'` once package-lock.json is committed.
+
+      - name: Install dependencies
+        # TODO: switch to `npm ci` once package-lock.json is committed.
+        run: npm install --no-audit --no-fund
+
+      - name: Build
+        run: npm run build

.github/workflows/deploy.yml

@@ -0,0 +1,53 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches:
+      - main
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages-deploy
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '24'
+          # TODO: add `cache: 'npm'` once package-lock.json is committed.
+
+      - name: Install dependencies
+        # TODO: switch to `npm ci` once package-lock.json is committed.
+        run: npm install --no-audit --no-fund
+
+      - name: Build
+        run: npm run build
+        env:
+          SITE_URL: https://tiennm99.github.io
+          SITE_BASE: /mathmax
+
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: ./build
+
+  deploy:
+    needs: build
+    runs-on: ubuntu-latest
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4