fix: merge agent command with args in parseAgents config

[log-li]

Summary

Fixes parseAgents() in src/config.ts to merge the args array with the command field when configuring agents in ~/.acpx/config.json.

Problem

When an agent is configured with both command and args:

{
  "agents": {
    "cursor": {
      "command": "/usr/local/bin/agent",
      "args": ["acp"]
    }
  }
}

The args field was silently ignored — only command was read. This caused the spawned agent to run without the required arguments, leading to ACP protocol initialization failures.

Changes

• src/config.ts: Updated parseAgents() to read raw.args, validate it as an optional string array, and merge it with command
• src/config.ts: Updated ConfigAgentEntry type to include args?: string[]
• test/config.test.ts: Added 3 new tests for args merging, backward compatibility, and validation

Testing

• All 443 tests pass (440 existing + 3 new)
• All lint checks pass
• Backward compatible: agents without args continue to work

Related

• Fixes fix: parseAgents() ignores 'args' field in ~/.acpx/config.json agents config #198
• Config schema inconsistency: acpx config show displays args as supported, but the field had no effect