Replace native alert()/confirm() with tpen-alert/tpen-confirm modal dialogs

[Copilot]

Native alert() and confirm() calls produce inconsistent, browser-controlled blocking dialogs. This replaces all instances across the codebase with the existing tpen-alert / tpen-confirm event-dispatch system.

Alert replacements

alert() → TPEN.eventDispatcher.dispatch('tpen-alert', { message })

Affected: annotorious-annotator/plain.js, roles-handler, projects/index.js, project-list-write.js, api/Project.js, manage-project/index.js

The permissions-denied alert in manage-project/index.js now defers the redirect via tpen-alert-acknowledged so the user sees the dialog before being navigated away.

Confirm replacements

All confirm() calls are replaced via a new utilities/confirmAction.js helper:

confirmAction(message, onConfirm, onCancel, { positiveButtonText, negativeButtonText })

The helper generates a unique confirmId (crypto.randomUUID() with a fallback) for each dialog. ConfirmContainer echoes the ID through button-click events; listeners use on() with an ID guard so stale callbacks from earlier dialogs never fire on a later one.

Affected: decline-project, leave-project, manage-layers, manage-pages, manifest-import, navigation-manager, quicktype-manager, roles-handler (3 instances), line-parser.js (3 instances), manage-project/index.js

ConfirmContainer improvements

• Stacking prevention: ignores new tpen-confirm requests while a dialog is already visible, preventing button-mash stacking.
• Keyboard accessibility: auto-focuses the positive button when a dialog opens; added :focus-visible CSS so the focused button has a visible outline, making tab/enter navigation work correctly.
• Contextual button labels: all call sites pass explicit positiveButtonText/negativeButtonText. Destructive or statement-style confirms use specific labels (e.g., Delete/Cancel, Leave/Cancel, Publish/Cancel, Transfer/Cancel, Discard/Keep Editing); question-style confirms keep the Yes/No defaults.

Methods that were async solely due to await confirm(…) patterns have had async/await removed from both the method and its call sites.

Original prompt

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This section details on the original issue you should resolve

<issue_title>alert() and confirm() where a dialog or modal makes more sense</issue_title>
<issue_description>There are a few things noted here that are out of scope but should be handled somewhere else.
...
3. Old pattern has alert() and confirm() where a dialog or modal makes more sense.</issue_description>

Comments on the Issue (you are @copilot in this section)

@thehabes See #327

• Fixes alert() and confirm() where a dialog or modal makes more sense #479

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