fix(i18n): register _ in all Jinja2 template instances, sync translation files, fix pipelines.html

- Register _() translation function in app/auth.py, app/api/local_auth.py, and
  app/api/billing.py template env globals to fix jinja2.exceptions.UndefinedError
- Update test_settings_template_has_db_wizard_link to assert i18n key instead of
  literal "DB Wizard" (template now uses {{ _("settings.db_wizard_btn") }})
- Add 418 missing en.json keys to all 30 non-English translation files as English
  fallbacks to fix test_all_languages_have_same_keys
- Fix orphan </template> tag in pipelines.html by adding missing
  <template x-if="pipelineModal.saving"> opening tag (fixes djlint H025)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_db_wizard_api.py

@@ -345,7 +345,7 @@ class TestSettingsPageWizardLink:
         template_path = Path(__file__).resolve().parent.parent / "frontend" / "templates" / "settings.html"
         content = template_path.read_text()
         assert "/database-wizard" in content
-        assert "DB Wizard" in content
+        assert "settings.db_wizard_btn" in content  # i18n key (resolves to "DB Wizard")
 
     def test_settings_template_has_help_link_rendering(self):
         """Test that the settings template renders help_link metadata."""