Build, publish to Gitea releases, and install the three extensions

Answers two things: how to install these without a marketplace, and how to keep
settings in sync when VS Code's Settings Sync cannot be pointed at Gitea.

- build.ps1 packages each extension into dist/
- publish.ps1 creates a release and uploads them, replacing same-named assets so a
  rolling "latest" tag stays clean
- install.ps1 downloads a release's assets and installs them, or -Local from dist/
- settings.ps1 copies User/ between the repo and the machine, and installs the
  marketplace extensions recorded in extensions.txt
- dev-link.ps1 junctions the sources into ~/.vscode/extensions for development
- ci-release.sh plus a Gitea Actions workflow do the build and publish on a tag push

Settings are copied, not symlinked: an atomic save replaces a symlink with a regular
file and the sync stops without looking broken.

vsce/ pins vsce and undici so packaging works on Node 18, which current vsce does not
support.

test/run.ps1 drives the real scripts against a stub of the Gitea release API. It
caught the multipart Content-Disposition being unquoted on .NET Framework, and
Invoke-WebRequest dropping the Authorization header across a redirect.

.gitea/workflows/release.yml

@@ -0,0 +1,51 @@
+# Packages the extensions and publishes them to a Gitea release.
+#
+# Needs a registered act_runner on the instance, and a GITEA_TOKEN secret with
+# write:repository plus read access to the extension repos. Gitea fetches the
+# actions/* actions from github.com unless the instance overrides
+# [actions] DEFAULT_ACTIONS_URL, so a locked-down instance may need those mirrored.
+#
+# ci-release.sh needs only bash, git, node and curl -- everything the runner image
+# already has once setup-node has run.
+#
+# The runner uses Node 20, which is also why CI is the easy way to build these:
+# vsce does not run on Node 18. See the README.
+
+name: Release extensions
+
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: 'Release tag to publish to'
+        required: false
+        default: 'latest'
+
+jobs:
+  release:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Package and publish
+        env:
+          GITEA_SERVER: ${{ github.server_url }}
+          GITEA_OWNER: ${{ github.repository_owner }}
+          GITEA_REPO: ${{ github.event.repository.name }}
+          GITEA_TOKEN: ${{ secrets.GITEA_TOKEN }}
+          # A tag push publishes to that tag; a manual run to whatever was asked for.
+          TAG: ${{ github.ref_type == 'tag' && github.ref_name || inputs.tag }}
+        run: bash scripts/ci-release.sh
+
+      - uses: actions/upload-artifact@v3
+        if: always()
+        with:
+          name: vsix
+          path: dist/*.vsix