fix: add basic auth for plugin client

[Slone123c]

What does this PR do?

• Add Basic Auth injection to the plugin client fetch when OPENCODE_SERVER_PASSWORD is set.
• Fix 401 Unauthorized errors for plugin-driven API calls (e.g., delegate_task/call_omo_agent) against a password-protected local server.

How did you verify your code works?

• Tested on local test cases.

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

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

Based on my search, I found one potentially related PR:

Related PR:

• fix(TUI): complete auth fix for TUI with server password (HTTP mode) #9095 - fix(TUI): complete auth fix for TUI with server password (HTTP mode)
  • This PR also addresses authentication issues with OPENCODE_SERVER_PASSWORD in HTTP mode. It may be related as both are fixing password-protected server auth issues, though fix(TUI): complete auth fix for TUI with server password (HTTP mode) #9095 specifically targets TUI while your PR targets the plugin client.

The other result (#6629) appears to be unrelated telemetry instrumentation work.