build: remove typescript.ignoreBuildErrors now that tsc is clean

tsc --noEmit reports 0 errors (was 586, all masked). next build now
type-checks on every build and prod deploy, so a type regression fails CI
instead of shipping. 649 tests green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

next.config.mjs

@@ -3,9 +3,6 @@ const nextConfig = {
   // 'standalone' bundles the app into a self-contained output for Docker deployments.
   output: process.env.DOCKER_BUILD ? 'standalone' : undefined,
 
-  typescript: {
-    ignoreBuildErrors: true,
-  },
   images: {
     unoptimized: true,
   },