feat: add public trial chat UI

[lpsmurf]

Summary

• add the public /try route with a dark mobile-first Poly trial chat UI
• add SSE consumer hook with quota, retry, tool-call rendering, and paywall triggers
• add paywall modal with Phantom connect/deeplink CTA and dev proxy for /api/chat to localhost:8787

Verification

• npm run build
• curl -I http://127.0.0.1:3000/try

Notes

• npm run typecheck still fails on pre-existing Agent/useProvisioning type drift outside the new trial files.

[lpsmurf]

@claude ready for review