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/implementation_plan.md

@@ -21,7 +21,8 @@ Claude Code → Gateway (Vercel) → OpenAI API
 ### Key Decisions
 
 - **Language**: Node.js with JavaScript (no TypeScript)
-- **Deployment**: Vercel serverless functions
+- **Framework**: Hono (multi-platform: Vercel, Cloudflare, Deno, Bun)
+- **Deployment**: Vercel serverless functions OR Cloudflare Workers
 - **Providers**: OpenAI first (via official SDK), others in TODO
 - **Config**: Environment variables only (no database)
 - **Auth**: Single shared token (user's `ANTHROPIC_AUTH_TOKEN` must match `GATEWAY_TOKEN`)
@@ -39,9 +40,15 @@ Claude Code → Gateway (Vercel) → OpenAI API
 ### File Structure
 
 ```
-api/v1/messages.js  - Main proxy handler
-package.json        - Dependencies (openai SDK)
-vercel.json         - Routing config
+src/
+├── index.js            - Hono app entry point
+├── routes/
+│   └── messages.js     - /v1/messages proxy handler
+api/
+└── index.js            - Vercel adapter
+package.json            - Dependencies (hono, openai)
+vercel.json             - Vercel config
+wrangler.toml           - Cloudflare Workers config
 ```
 
 ### How to apply: When adding new providers or modifying the gateway, follow the established pattern in `api/v1/messages.js` for request/response transformation.