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>

frontend/templates/pipelines.html

@@ -317,8 +317,9 @@
             class="px-4 py-2 text-sm font-medium text-white bg-blue-600 hover:bg-blue-700 disabled:opacity-60 rounded-md"
             style="min-height:44px;"
           >
-              <i class="fas fa-spinner fa-spin mr-1" aria-hidden="true"></i>
-            </template>
+              <template x-if="pipelineModal.saving">
+                <i class="fas fa-spinner fa-spin mr-1" aria-hidden="true"></i>
+              </template>
             <span x-text="pipelineModal.editMode ? 'Save Changes' : 'Create'"></span>
           </button>
         </div>