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).

scripts/extract-release-section.test.mjs

@@ -0,0 +1,26 @@
+import { describe, it } from 'node:test';
+import assert from 'node:assert/strict';
+import { findReleaseSection } from './extract-release-section.mjs';
+
+const FIXTURE = `
+## [1.48.0] - 2026-06-10
+
+## Highlights
+- One
+
+## [1.47.0]
+- Old
+`;
+
+describe('findReleaseSection', () => {
+  it('matches base line for -rc versions', () => {
+    const entry = findReleaseSection(FIXTURE, '1.48.0-rc.3');
+    assert.equal(entry.headerVersion, '1.48.0');
+    assert.match(entry.body, /Highlights/);
+  });
+
+  it('matches base line for -dev versions', () => {
+    const entry = findReleaseSection(FIXTURE, '1.48.0-dev');
+    assert.equal(entry.headerVersion, '1.48.0');
+  });
+});