fix(settings): save the guest allowlist again

[ernolf]

Summary

The Guests admin settings page no longer persisted changes to the app allowlist.

Cause

The allowlist NcSelect still used @input="saveConfig", which @nextcloud/vue 9 no longer emits (the same Vue 3 migration regression as #1323, and the allowlist-selector remainder of #995 that #1598 did not cover, since #1598 only fixed the on/off switches). Editing the list of allowed apps therefore sent no PUT /apps/guests/config and was lost on reload.

Change

The selector is reworked to the inline-edit pattern used in Accounts management:

• The current allowlist is shown read-only as wrapping chips (the full list stays visible, no truncation) with an edit (pencil) button, indented under the "Limit guest access to an app's allowlist" switch it belongs to.
• Clicking the pencil opens the NcSelect; edits go to a draft. A confirm (check) button applies the draft and saves. Closing the dropdown no longer saves on its own, and the save no longer relies on the dead @input event.
• The reset button keeps working and now also refreshes the draft while editing.

Split out of #1602 so it can be backported on its own. The default-quota feature from that PR follows as a separate PR once this one lands.

Fixes #1591

Testing

• Add and remove apps, confirm with the check button, reload: the selection persists.
• Toggling the switch and the reset button still work.

🤖 AI (if applicable)

• The content of this PR was partly generated using AI
  Assisted-by: ClaudeCode:claude-opus-4-8

Screenshots:

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[pringelmann]

Thank you for splitting this out :) I found one UI regression that is easy to fix, but otherwise looks good!

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