refactor: replace legacy delete-button with link-action (#38143)

Removes the legacy `delete-button` handler (`initGlobalDeleteButton`)
and migrates all remaining usages to `link-action` and `show-modal` /
`form-fetch-action`.

Two handlers are adjusted for the new request shape: webauthn key delete
reads `id` from the query, and account deletion returns `JSONError` on
validation failure.

A E2E test ist added to cover one of the use cases.

Suggested in
https://github.com/go-gitea/gitea/pull/38046#discussion_r3414936737.

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: bircni <bircni@icloud.com>

web_src/js/index.ts

@@ -58,7 +58,7 @@ import {initAdminSelfCheck} from './features/admin/selfcheck.ts';
 import {initOAuth2SettingsDisableCheckbox} from './features/oauth2-settings.ts';
 import {initGlobalFetchAction} from './features/common-fetch-action.ts';
 import {initCommmPageComponents, initGlobalComponent, initGlobalDropdown, initGlobalInput} from './features/common-page.ts';
-import {initGlobalButtonClickOnEnter, initGlobalButtons, initGlobalDeleteButton} from './features/common-button.ts';
+import {initGlobalButtonClickOnEnter, initGlobalButtons} from './features/common-button.ts';
 import {initGlobalComboMarkdownEditor, initGlobalEnterQuickSubmit, initGlobalFormDirtyLeaveConfirm} from './features/common-form.ts';
 import {callInitFunctions} from './modules/init.ts';
 import {initRepoViewFileTree} from './features/repo-view-file-tree.ts';
@@ -81,7 +81,6 @@ const initPerformanceTracer = callInitFunctions([
   initGlobalEnterQuickSubmit,
   initGlobalFormDirtyLeaveConfirm,
   initGlobalComboMarkdownEditor,
-  initGlobalDeleteButton,
   initGlobalInput,
   initGlobalShortcut,