Add a Gitea Actions CI workflow

Ruby syntax check, a require_relative "app" smoke load, and JS syntax
check on every push/PR. No test suite exists yet, so these are cheap
syntax/load checks rather than behavioral tests.

.gitea/workflows/ci.yml

@@ -0,0 +1,29 @@
+name: CI
+
+on:
+  push:
+  pull_request:
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: file # reads .ruby-version
+          bundler-cache: true
+
+      - name: Ruby syntax check
+        run: find app.rb config lib -name "*.rb" -print0 | xargs -0 -n1 ruby -c
+
+      - name: App loads without errors
+        run: bundle exec ruby -e 'require_relative "app"'
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+
+      - name: JS syntax check
+        run: find public/js -name "*.js" -print0 | xargs -0 -n1 node --check