fix(tui): render Windows file:// plugin names correctly in /status

[JasonJason-oy]

Issue for this PR

Closes #40131

Type of change

• Bug fix

What does this PR do?

On Windows, /status derived the plugin name by splitting the fileURLToPath() result on "/", which does not split backslash paths. The whole path became the "filename" and was truncated at the first dot (e.g. "C:\Users\me" for a plugin under the home directory). This PR splits on both "/" and "" so the last path segment (the plugin file name) is used on every platform. The index.ts fallback (parent directory name) is unchanged.

How did you verify your code works?

Verified the derived names with Node for both path styles:

• file:///C:/Users/me/.config/opencode/plugins/superpowers.js -> superpowers (was "C:\Users\me")
• file:///home/me/.config/opencode/plugins/superpowers.js -> superpowers (unchanged)
• file:///home/me/.config/opencode/plugins/my-plugin/index.ts -> my-plugin (unchanged)
• oh-my-openagent@latest -> oh-my-openagent @latest (unchanged)

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR