trim: remove dead code and move large spec docs to attic

- Remove unused exports: renderProgress, formatTripleBoundaryCounterexample, clearCapturedRoutes
- Remove dead BUILTIN_PLUGIN_CONTRACTS constant (auto-registration removed earlier)
- Fix app-loader error messages to mention multiple export patterns
- Move to attic: protocol-extensions-spec, OUTBOUND_CONTRACT_MOCKING_SPEC, PLUGIN_CONTRACTS_SPEC, fastify-structure
- Build: clean | Tests: 849 pass, 0 fail

src/cli/commands/doctor/checks/routes.ts

@@ -116,8 +116,8 @@ export async function checkRouteDiscovery(options: RouteCheckOptions): Promise<R
         name: 'route-discovery',
         status: 'fail',
         message: `App file ${appFile} does not export a valid object.`,
-        detail: 'Ensure the app file exports a Fastify instance as default.',
-        remediation: 'Export your Fastify instance as default: export default app;',
+        detail: 'Ensure the app file exports a Fastify instance or a factory function.',
+        remediation: 'Export your Fastify instance: export default app; or export const createApp = () => app; or module.exports = app;',
         mode: 'all',
       };
     }