Windows changelog fragments

Post-update "what's new" changelog, mirroring desktop/macos/changelog/.

Authoring

Add one fragment per user-visible change under unreleased/, named YYYY-MM-<slug>.json, using the same schema as the macOS app:

{ "changes": ["Short, user-facing sentence.", "Another change."] }

{ "change": "single line" } is also accepted. Keep lines short — they render in a 360×168 acrylic toast (src/renderer/src/components/insight/InsightToast.tsx), with the full list one click away via "View release notes".

Runtime

On launch, src/main/whatsNew.ts compares the running build to the last version whose notes were shown (lastShownChangelogVersion in app-settings.json) and, only when it increased (a real update — never a fresh install), surfaces the current fragment(s) in the shared toast window. AUMID is set before the toast, so packaged notifications attribute to Omi.

Deferred (tracked follow-up)

The macOS desktop-changelog.py consolidation (fragments → releases/<version>.json on release) and its CI check (check-desktop-changelog.py) are not yet ported. Today whatsNew.ts imports the single unreleased fragment directly. When a Windows release pipeline lands, port the consolidation script + a CI gate that fails a PR whose user-visible change ships no fragment, and switch whatsNew.ts to read the compiled per-version file.