Decide where @nextcloud/dialogs is taught, then write it

@nextcloud/dialogs (showSuccess / showError) was identified as a gap on 2026-06-11 and deliberately deferred out of the beginner track — but it was never placed in a module.

So unlike Initial State and IAppConfig, this one has no home in the manifest yet. This issue is a decision first, content second.

Why not beginner

It is a polish layer, not a core concept. Beginner can use console.log or a simple DOM update to show feedback; toasts are the "proper Nextcloud UX pattern" introduced once the app works.

The decision

Where does it go? Candidates discussed:

• php-i-12 / Frontend Performance and UX, which exists in the manifest
• alongside the Vue component work at intermediate
• a standalone module on the design system / UX patterns (standalone-design-system exists)

Then write it, mirrored across both tracks.

Done when

It has a home in the manifest and content there, or a recorded decision that it is not taught.

Part of #16.

Start by reading the manifest entries for php-i-12, standalone-design-system, and the intermediate Vue component track, along with the discussion in #16. Record the placement decision, add the @nextcloud/dialogs content in both tracks if taught, and verify the manifest and content satisfy the stated done condition.