Add CI workflow with composite actions (#6)

Uses org-level composite actions for clean status check names.
Jobs skip gracefully when no package.json present.

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

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: sylvansys

.github/workflows/ci.yml

@@ -0,0 +1,28 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+    types: [opened, synchronize, reopened]
+  merge_group:
+
+jobs:
+  Lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: constellos/.github/actions/lint@main
+
+  Typecheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: constellos/.github/actions/typecheck@main
+
+  Unit-Tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: constellos/.github/actions/unit-tests@main