ci: Add tag-triggered release workflow

Bumping the version, committing, and tagging \`vx.y.z\` should be the
entire release ritual — the rest is mechanical. Add
\`.github/workflows/release.yml\` that fires on \`v*\` tag pushes, runs
\`make dist\` on a macos-14 runner, and creates a GitHub Release with
the DMG attached.

Release notes use \`gh release create --generate-notes\`, which derives
them from PR titles merged since the previous tag (same algorithm as
the "Generate release notes" button in the GitHub UI). This removes
the manual \`make dist\` + \`gh release create\` steps from the release
flow entirely.

The workflow needs \`contents: write\` to create the release; no other
permissions or secrets are required since \`GITHUB_TOKEN\` covers the
release API surface.

Author: cuiko

.github/workflows/release.yml

@@ -0,0 +1,26 @@
+name: release
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+jobs:
+  release:
+    runs-on: macos-14
+    permissions:
+      contents: write
+    steps:
+      - uses: actions/checkout@v4
+      - name: Show toolchain
+        run: swift --version
+      - name: Build DMG
+        run: make dist
+      - name: Create GitHub Release
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release create "${GITHUB_REF_NAME}" \
+            dist/TermIMS.dmg \
+            --title "${GITHUB_REF_NAME}" \
+            --generate-notes