fix(tui): directory handling in AttachCommand

[aryasaatvik]

Fixes ENOENT errors when attaching to remote opencode servers.

The v1.1.1 attach command always sent the client's cwd to the server via x-opencode-directory header. For remote servers, this path doesn't exist, causing MCP connections, bash tool and more execution to fail with ENOENT.
Now directory is only sent when --dir is explicitly provided, letting the server use its own cwd by default.

related #6715

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Summary

No duplicate PRs found. The PR you're creating appears to be unique.

However, I found related PRs that address similar concerns with the attach command:

1. PR fix: pass --dir parameter from attach command to server #6413 - fix: pass --dir parameter from attach command to server

   • Also deals with directory handling in the attach command

2. PR feat: show remote host and cwd in taskbar when using attach #4827 - feat: show remote host and cwd in taskbar when using attach

   • Related to cwd handling in remote attach scenarios

These PRs touch on related functionality but appear to address different aspects. Make sure to review them to ensure your fix doesn't conflict with existing solutions and aligns with the overall directory handling strategy.

[aryasaatvik]

@rekram1-node can you take a look? remote opencode connections are broken in v1.1.1