fix(e2e): disable Astro Dev Toolbar during landing e2e tests

The Astro Dev Toolbar (enabled by default in dev mode) injects h1
elements ("No islands detected", "Audit", "Settings") and a
"Community" link inside its shadow DOM. Playwright CSS selectors
pierce shadow DOM, causing 6 test failures:

- 5 heading-hierarchy tests saw extra h1 elements from the toolbar
- footer "Community" column title resolved to 2 elements (footer h4
  plus toolbar's Astro community chat link)

Root-cause fix: set PLAYWRIGHT=1 env var in the Playwright webServer
command; Astro config conditionally disables devToolbar when set.
Normal development retains the toolbar.

playwright.landing.config.ts

@@ -22,7 +22,7 @@ export default defineConfig({
     },
   ],
   webServer: {
-    command: `cd apps/landing && npx astro dev --port ${LANDING_PORT}`,
+    command: `cd apps/landing && PLAYWRIGHT=1 npx astro dev --port ${LANDING_PORT}`,
     port: LANDING_PORT,
     reuseExistingServer: !process.env.CI,
     timeout: 60_000,