feat: add a web-ready blank starter with managed analytics and optional AI

[xiongxz]

Summary

• add a real blank Vite + React web starter with the InsForge SDK and runtime-config support
• include an opt-in authenticated ai-chat Edge Function and browser helper that use the existing platform-managed AI runtime; no new AI toggle or provider credential is introduced
• make every existing template recognize platform-managed GA4 initialization so page views are not duplicated
• strengthen the analytics contract check to enforce the duplicate-prevention handshake

Dependency and rollout

Depends on lexmount/insforge-platform#96. Deploy that platform change before synchronizing and publishing this new blank template version, because it also promotes the legacy built-in blank entry to the official repository source.

Validation

• registry validation: 15 templates passed
• validator unit tests: 23 passed
• GA4 contract validation: 15 templates passed
• deno check blank/functions/ai-chat.ts
• production build + artifact admission passed for every native template: blank, admin-dashboard, insight-flow-agent-chat, web-research-agent, website-change-monitor, react, and todo