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).

.github/workflows/reusable-channel-publish.yml

@@ -176,18 +176,32 @@ jobs:
       - name: extract changelog
         id: changelog
         run: |
+          set -euo pipefail
           VERSION="${{ steps.get-version.outputs.version }}"
-          BODY=$(awk "/^## \[$VERSION\]/{found=1; next} found && /^## \[/{exit} found{print}" CHANGELOG.md)
-          if [ -z "$BODY" ]; then
-            BASE_VERSION="$(node -e 'const v=process.argv[1]; const m=v.match(/^(\d+\.\d+\.\d+)/); if(m){process.stdout.write(m[1]);}' "$VERSION")"
-            if [ -n "$BASE_VERSION" ] && [ "$BASE_VERSION" != "$VERSION" ]; then
-              BODY=$(awk "/^## \[$BASE_VERSION\]/{found=1; next} found && /^## \[/{exit} found{print}" CHANGELOG.md)
-            fi
+          BODY=""
+          if node scripts/extract-release-section.mjs CHANGELOG.md "$VERSION" --allow-empty > /tmp/changelog-body.md; then
+            BODY="$(cat /tmp/changelog-body.md)"
           fi
           EOF_MARKER=$(dd if=/dev/urandom bs=15 count=1 status=none | base64)
           echo "body<<$EOF_MARKER" >> "$GITHUB_OUTPUT"
           echo "$BODY" >> "$GITHUB_OUTPUT"
           echo "$EOF_MARKER" >> "$GITHUB_OUTPUT"
+      - name: extract what's new for release asset
+        id: whats-new
+        run: |
+          set -euo pipefail
+          VERSION="${{ steps.get-version.outputs.version }}"
+          CHANNEL="${{ inputs.channel }}"
+          if ! node scripts/extract-release-section.mjs WHATS_NEW.md "$VERSION" > /tmp/whats-new.md; then
+            if [ "$CHANNEL" = "release" ]; then
+              echo "::error::WHATS_NEW.md has no section for version $VERSION (required for stable release)"
+              exit 1
+            fi
+            echo "::warning::WHATS_NEW.md has no section for $VERSION — skipping whats-new.md asset"
+            echo "skip=true" >> "$GITHUB_OUTPUT"
+            exit 0
+          fi
+          echo "skip=false" >> "$GITHUB_OUTPUT"
       - name: create or update release
         id: create-release
         uses: actions/github-script@v9
@@ -237,6 +251,14 @@ jobs:
               prerelease,
             });
             return data.id;
+      - name: upload whats-new.md release asset
+        if: steps.whats-new.outputs.skip != 'true'
+        env:
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: |
+          set -euo pipefail
+          RELEASE_TAG="${{ steps.tag.outputs.value }}"
+          gh release upload "$RELEASE_TAG" /tmp/whats-new.md --clobber
 
   build-macos-windows:
     if: ${{ inputs.build_platform_artifacts }}