feat(hono): add generic Env type support to createMcpHonoApp

[dagangtj]

Summary

This PR adds generic type support to `createMcpHonoApp` to allow users to specify custom Env types, enabling proper type inference for environment bindings (like Cloudflare D1) and variables within MCP handlers.

Changes

• Add generic type parameter `E extends BlankEnv = BlankEnv` to `createMcpHonoApp`
• Pass generic type to `Hono` constructor for proper type inference
• Update `Context` type to `Context` for typed middleware support
• Add usage example in JSDoc showing Cloudflare Workers pattern
• Add tests for generic type support and backward compatibility

Usage Example

```typescript
// With custom Env type for Cloudflare Workers
type Env = {
Bindings: {
DB: D1Database;
};
Variables: {
user: User;
};
};

const app = createMcpHonoApp();

app.get('/data', async (c) => {
const db = c.env.DB; // typed as D1Database
const user = c.get('user'); // typed as User
// ...
});
```

Backward Compatibility

This change is fully backward compatible - existing code using `createMcpHonoApp()` without a generic parameter will continue to work exactly as before (defaults to `BlankEnv`).

Related Issue

Fixes #1877

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