[FEATURE]: Allow using $HOME variable in tui.json plugin path

[flexdinesh]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Currently the plugin paths in tui.json only works if the path is absolute. Would make it easier to manage dotfiles across different machines with different users if the path would work with $HOME variable expansion.

Current:

{
  "plugin": [
    "/home/myuser/workspace/oc-timer/tui.tsx",
    "/home/myuser/workspace/tokeninspector/plugins/opencode-tui/oc-tokeninspector.tsx"
  ]
}

Proposed:

{
  "plugin": [
    "$HOME/workspace/oc-timer/tui.tsx",
    "$HOME/workspace/tokeninspector/plugins/opencode-tui/oc-tokeninspector.tsx"
  ]
}

[github-actions]

This issue might be related to existing issues requesting similar functionality. Please check:

• [FEATURE]: Support ~ and $HOME expansion in permission patterns #9806: Feature request for ~ and $HOME expansion in permission patterns in opencode.jsonc — same underlying need for home directory variable expansion in config paths
• Glob patterns with ~/ expansion don't work in instructions configuration #3289: Bug where glob patterns with ~/ don't work in the instructions configuration

These cover different config keys but the same root ask (expand $HOME/~ in config file paths). It may be worth consolidating or linking these.