Fix: Pass environment variables to codex MCP process

Problem

When running happy codex with custom environment variables configured in ~/.codex/config.toml, the command fails with "Missing environment variable: MY_ENV_KEY" error.

Steps to Reproduce:

1. Add env_key = "MY_ENV_KEY" to ~/.codex/config.toml
2. Set environment variable: export MY_ENV_KEY="some_value"
3. Run happy codex
4. Error: "Missing environment variable: MY_ENV_KEY"

Solution

The StdioClientTransport constructor was not passing environment variables to the codex subprocess. Added proper environment variable inheritance in src/codex/codexMcpClient.ts.

Code Changes:

// Before
this.transport = new StdioClientTransport({
    command: 'codex',
    args: ['mcp']
});

// After  
this.transport = new StdioClientTransport({
    command: 'codex',
    args: ['mcp'],
    env: Object.keys(process.env).reduce((acc, key) => {
        const value = process.env[key];
        if (typeof value === 'string') acc[key] = value;
        return acc;
    }, {} as Record<string, string>)
});

Testing

• ✅ happy codex now starts without environment variable errors
• ✅ Custom environment variables properly inherited by codex process
• ✅ No breaking changes

Type of Change

• Bug fix (non-breaking change which fixes an issue)

Fixes #[ISSUE_NUMBER] (if applicable)