refactor: Migrate to Hono framework for multi-platform support

- Replace Vercel-specific handler with Hono framework
- Add Cloudflare Workers support via wrangler.toml
- Restructure project: src/index.js, src/routes/messages.js
- Update README with Cloudflare deployment instructions
- Save framework decision to memory

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.claude/memory/framework_decision.md

@@ -0,0 +1,26 @@
+---
+name: Framework Decision - Hono
+description: Why Hono was chosen over alternatives for the gateway
+type: project
+---
+
+## Framework Choice: Hono
+
+**Decision:** Use Hono as the web framework for Claude Central Gateway.
+
+**Why Hono over alternatives:**
+
+| Alternative | Why not |
+|-------------|---------|
+| Nitro | Overkill for simple proxy, 200KB+ bundle vs 14KB |
+| itty-router | Cloudflare-focused, Vercel needs adapter |
+| Native | Duplicate code per platform, manual streaming |
+
+**Why Hono:**
+- Single codebase for Vercel + Cloudflare + Deno + Bun
+- Ultra-lightweight (~14KB)
+- First-class streaming support (critical for SSE)
+- Zero-config multi-platform
+- Aligns with project philosophy: "Minimal, simple, deploy anywhere"
+
+**How to apply:** All API routes should use Hono's `app.route()` pattern. Keep handlers simple and stateless.