feat(FN-3234): refactor test-changed script and add workflow tests

This merge refactors the test-changed script and adds new CLI tests (FN-3234), keeping automation on the full-suite path. It includes a new test file for the root test command, updates to the CI workflow, and documentation improvements.

Fusion-Task-Id: FN-3234

.github/workflows/pr-checks.yml

@@ -38,5 +38,5 @@ jobs:
       - name: Typecheck
         run: pnpm typecheck
 
-      - name: Test
-        run: pnpm test
+      - name: Test (full suite)
+        run: pnpm test:full