ci(forgejo): add proof CI workflow for Forgejo Actions

First step of porting CI/CD from GitHub Actions to the self-hosted
Forgejo at git.ullrich.is. Proves the trails-forgejo runner executes
a real job (checkout + pnpm + typecheck) before porting the full suite.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -0,0 +1,24 @@
+name: CI
+# Forgejo Actions port — proof workflow. Once green, the remaining jobs from
+# .github/workflows/ci.yml (lint, test, build, e2e, visual, image-smoke, security)
+# get ported here. NOTE: Forgejo uses .forgejo/workflows in preference to
+# .github/workflows, so the GitHub copies do not double-run here.
+on:
+  push:
+    branches: [main, ci/forgejo-actions]
+  pull_request:
+    branches: [main]
+
+jobs:
+  typecheck:
+    name: Typecheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v7
+      - uses: pnpm/action-setup@v6
+      - uses: actions/setup-node@v6
+        with:
+          node-version: 24
+          cache: pnpm
+      - run: pnpm install --frozen-lockfile
+      - run: pnpm typecheck