fix(app-showcase): stamp inquiry source only when absent (verify fidelity)

The guest-defaults hook unconditionally set source='web', so the verify
round-trip wrote source='verify-sample' and read back 'web' — a fidelity
gap that failed the Dogfood Regression Gate. Make it a default (only when
absent), matching status. Public submissions never include source (the
form whitelist excludes it), so they still get 'web'; explicit values now
round-trip cleanly.

Author: claude

examples/app-showcase/src/hooks/index.ts

@@ -94,7 +94,7 @@ export const StampInquiryDefaultsHook = {
   events: ['beforeInsert'] as LifecycleEvent[],
   body: {
     language: 'js' as const,
-    source: "if (!ctx.input.status) ctx.input.status = 'new'; ctx.input.source = 'web';",
+    source: "if (!ctx.input.status) ctx.input.status = 'new'; if (!ctx.input.source) ctx.input.source = 'web';",
   },
   priority: 50,
   onError: 'abort' as const,