Remove the WebView terminal renderer: xterm on web, native grid on mobile (#7639)

* refactor(terminal): remove the WebView terminal renderer

Native uses the native grid renderer only; web keeps xterm. The legacy
renderer setting, its diagnostics toggle, the esbuild WebView bundle and
its CI drift check are gone.

* test(terminal): target the visible terminal surface in the file paste spec

A second page opening a terminal in the same workspace adds a retained,
hidden surface to the first page, so the unscoped locator matched two
textareas and failed strict mode.

* test(server): wait for the shortstat warm instead of polling 500ms

The background warm shells out to git; on Windows CI that regularly
outlasts the 20x25ms poll and fails the test. Use the completion callback
the warm already exposes and keep the non-blocking check.

.github/workflows/ci.yml

@@ -415,9 +415,7 @@ jobs:
         run: npm run build:app-deps
 
       - name: Run app unit tests
-        run: |
-          npm run check:terminal-webview --workspace=@getpaseo/app
-          npm run test --workspace=@getpaseo/app
+        run: npm run test --workspace=@getpaseo/app
 
       - uses: actions/setup-java@v4
         with: