fix: use platform-aware local defaults

- Route app DB and sqlite-vec defaults through shared platform helpers
- Mirror platform DB defaults in the standalone MCP package
- Fix Windows setup npm spawning and remove macOS-only env defaults

scripts/dev/setup-local.mjs

@@ -6,8 +6,14 @@ function run(command, args) {
   const result = spawnSync(command, args, {
     stdio: 'inherit',
     env: process.env,
+    shell: process.platform === 'win32',
   });
 
+  if (result.error) {
+    console.error(`[setup-local] Failed to run ${command}: ${result.error.message}`);
+    process.exit(1);
+  }
+
   if (result.status !== 0) {
     process.exit(result.status || 1);
   }