feat(whats-new): remote release notes with dev workspace mode (#1058)

* feat(whats-new): remote release notes with dev workspace mode

Add WHATS_NEW.md, CI whats-new.md asset upload, and client fetch/cache
with embedded fallbacks. Dev and -dev builds read the full file from the
repo for debugging; RC/stable download the release asset on first use.

* fix(whats-new): render ## headings and add changelog tab

Parse h2 sections in release-notes markdown; load changelog alongside
highlights and let users switch views on the What's New page.

* fix(whats-new): prefetch on startup and fix CI typecheck prebuild

Prefetch whats-new asset when the shell loads on RC/stable builds.
Run prebuild:release-notes before tsc and coverage jobs so the
gitignored generated bundle exists in CI.

* docs: CHANGELOG and credits for What's New remote notes (PR #1058)

* fix(whats-new): always slice embedded release notes to current line

Drop full CHANGELOG embed for -dev bundles; tauri:dev still reads live
markdown from the repo. Ignore all of src/generated/ in git.

* fix(whats-new): fetch release asset via Rust to bypass CORS

Route whats-new.md download through fetch_url_bytes; rename the
technical tab label; add fetch unit tests (PR #1058 review).

RELEASE_PROCESS.md

@@ -49,6 +49,7 @@ Rules:
 
 ### Step B: Promote to RC (`next`)
 
+0. Confirm `WHATS_NEW.md` has a `## [X.Y.Z]` section for the release line about to ship (user-facing copy for the in-app What's New screen; CI uploads it as `whats-new.md` on the release tag).
 1. Run workflow: **Promote main to next**.
 2. Workflow behavior:
    - validates required `main` checks before promotion (default: `ci-ok`, or UI-style `ci-main / ci-ok`; either satisfies the gate)