fix: typecheck without emit, placeholder test, drop build artifacts

Removes composite project references in favor of simpler -p checking.
Adds noEmit to tsconfig so tsc is typecheck-only.
Adds smoke test to unblock CI test gate.
Ignores tsbuildinfo artifacts from git.

tsconfig.base.json

@@ -6,7 +6,7 @@
     "target": "ES2022",
     "types": ["bun-types"],
     "skipLibCheck": true,
-    "composite": true,
+    "noEmit": true,
     "verbatimModuleSyntax": true
   }
 }