Upgrade to Astro 7

Upgrade astro and @astrojs/mdx to v7 (Vite 8, Rust compiler, rolldown).

- Add .npmrc legacy-peer-deps: several third-party integrations
  (astro-embed, @lucide/astro, astro-auto-import, astro-favicons,
  @playform/compress, astro-seo) still cap peers at Astro 6, so npm ci
  fails with ERESOLVE without it. They work fine at runtime.
- BaseLayout.astro: convert a multi-line HTML comment to a JSX comment;
  the stricter Rust compiler rejected the apostrophes/quotes inside it.
- playwright.config.ts: local webServer now builds + previews instead of
  `astro dev`, which self-daemonizes in v7 (broke `npm run test:e2e`) and
  matches what CI already runs.

Playwright stays at 1.60.0 on purpose: 1.61.0's headless shell stalls
requestAnimationFrame after a client-side DOM swap, timing out nav e2e
tests. Astro 7 itself is unaffected.

Verified: build, astro check (0/0/0), 1676 vitest, 341 e2e (0 failed),
npm ci, and a cold `npm run test:e2e` all pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: benbalter

.npmrc

@@ -0,0 +1,7 @@
+# Several third-party Astro integrations (astro-embed, @lucide/astro,
+# astro-auto-import, astro-favicons, @playform/compress, astro-seo) declare peer
+# dependencies that cap at Astro 6 but work fine with Astro 7's stable
+# integration API. legacy-peer-deps lets `npm install`/`npm ci` resolve without
+# ERESOLVE failures here and in CI/Cloudflare builds. Remove once these
+# integrations ship Astro 7 peer ranges.
+legacy-peer-deps=true