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.

package.json

@@ -3,7 +3,7 @@
   "private": true,
   "workspaces": ["server", "web", "shared"],
   "scripts": {
-    "typecheck": "bunx tsc -b server shared",
+    "typecheck": "bunx tsc -p server && bunx tsc -p shared",
     "test": "bun test server"
   },
   "devDependencies": {