Enable Jinja2 autoescaping (#200)

- Enable Jinja2 autoescape by default in the template environment.
- Use json.dumps to safely inject sso_name into JavaScript context.
- Fix linting issue (line too long) in injected_auth_page.py.
- Update tests to verify escaping and safe injection.

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Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>
Co-authored-by: werdnum <271070+werdnum@users.noreply.github.com>

tests/test_hass_webserver.py

@@ -149,3 +149,4 @@ async def test_frontend_injection(hass: HomeAssistant, hass_client):
     text = await resp.text()
 
     assert "<script src='/auth/oidc/static/injection.js" in text
+    assert "window.sso_name = \"OpenID Connect (SSO)\";" in text