feat(updater): reusable "What's new" dialog promoting features on update

[remcostoeten]

Goal

Build a reusable "What's new" dialog that promotes new features when an update is available/applied.

Context (re-scoped 2026-07-31)

The original research half of this ticket is done: the Tauri auto-updater shipped and the macOS updater channel went live in v0.38.1 (PR #224). What remains is the product surface on top of it.

Scope

• Reusable dialog component that highlights new features after an update is applied (and optionally when one is available).
• Source release notes from the existing changelog data (packages/studio/src/features/sidebar/changelog-data.ts).
• Decide update-check cadence and opt-in/opt-out for the promo dialog itself.

Deliverable

The dialog component wired to the updater events + changelog data.