fix: correct archive checksum and automate CI updates (#1)

## Summary
- Fix the v0.0.1 archive checksum in `artifacthub-pkg.yml` to match the actual GitHub release tarball (was causing "Checksum mismatch" on Headlamp plugin install)
- Gitea CI now computes the checksum after packaging and updates `artifacthub-pkg.yml` on `main` via the Gitea API, then uploads the **same tarball** to GitHub releases (requires `GH_PAT` secret) so both releases serve identical artifacts
- GitHub CI becomes a fallback — skips entirely if the Gitea CI already created the release, preventing a second build from producing a mismatched tarball

## Setup required
Add a `GH_PAT` secret to the Gitea repo containing a GitHub personal access token with `repo` scope. Without it, the GitHub release step gracefully skips and the GitHub Actions fallback handles it.

## Test plan
- [ ] Verify `GH_PAT` secret is set in Gitea repo settings
- [ ] Tag and push a new release (`v0.0.2`)
- [ ] Confirm Gitea CI updates `artifacthub-pkg.yml` checksum on `main`
- [ ] Confirm GitHub release is created by Gitea CI with matching tarball
- [ ] Confirm GitHub Actions fallback skips (release already exists)
- [ ] Verify Headlamp plugin installs without checksum mismatch

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Chris Farhood <chris@farhood.org>
Reviewed-on: farhoodliquor/polaris-headlamp-plugin#1
Co-authored-by: claude <no-reply.claude@farh.net>
Co-committed-by: claude <no-reply.claude@farh.net>

.github/workflows/release.yml

@@ -1,4 +1,4 @@
-name: GitHub Release
+name: GitHub Release (fallback)
 
 on:
   push:
@@ -12,25 +12,44 @@ jobs:
   release:
     runs-on: ubuntu-latest
     steps:
+      - name: Check if release already exists
+        id: check
+        run: |
+          if gh release view "${{ github.ref_name }}" --repo "${{ github.repository }}" &>/dev/null; then
+            echo "Release ${{ github.ref_name }} already exists (created by Gitea CI), skipping."
+            echo "exists=true" >> "$GITHUB_OUTPUT"
+          else
+            echo "No existing release found, building as fallback."
+            echo "exists=false" >> "$GITHUB_OUTPUT"
+          fi
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+
       - name: Checkout
+        if: steps.check.outputs.exists == 'false'
         uses: actions/checkout@v4
 
       - name: Setup Node.js
+        if: steps.check.outputs.exists == 'false'
         uses: actions/setup-node@v4
         with:
           node-version: '20'
           cache: 'npm'
 
       - name: Install dependencies
+        if: steps.check.outputs.exists == 'false'
         run: npm ci
 
       - name: Build plugin
+        if: steps.check.outputs.exists == 'false'
         run: npx @kinvolk/headlamp-plugin build
 
       - name: Package tarball
+        if: steps.check.outputs.exists == 'false'
         run: npx @kinvolk/headlamp-plugin package
 
       - name: Create GitHub Release
+        if: steps.check.outputs.exists == 'false'
         uses: softprops/action-gh-release@v2
         with:
           files: "*.tar.gz"