refactor: add main.ts decomposition guardrails and extract core helpers

.github/workflows/ci.yml

@@ -32,9 +32,15 @@ jobs:
       - name: Build (TypeScript check)
         run: pnpm run build
 
+      - name: Main.ts line gate (baseline)
+        run: pnpm run check:main-lines:baseline
+
       - name: Config tests
         run: pnpm run test:config
 
+      - name: Core tests
+        run: pnpm run test:core
+
       - name: Security audit
         run: pnpm audit --audit-level=high
         continue-on-error: true