fix(desktop): support Bun plugin runtime APIs

[askforoneZY]

Issue for this PR

Closes #25880

Related: #25824, #28287, code-yeongyu/oh-my-openagent#4662

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Desktop runs server plugins inside Electron's Node sidecar, so Bun-targeted plugins can fail before their config hooks register agents or commands. This PR adds a small compatibility layer for the Bun runtime APIs hit by current desktop plugin failures (Bun.serve and Bun.which).

It also initializes plugin config hooks before the agent and command catalogs are built. That lets plugin-provided agents and slash commands appear in Desktop after the plugin loads.

How did you verify your code works?

• Reproduced the Desktop sidecar showing only built-in agents/commands while the plugin was configured.
• Reproduced the plugin load failure from oh-my-openagent@4.6.0 requiring Bun.serve under Electron/Node.
• Rebuilt the opencode Node sidecar bundle and verified the Electron-run sidecar listed OMO agents and commands, including /start-work.
• Ran bun.cmd typecheck from packages/opencode in the original package workspace after the same source changes.
• Ran git diff --check on this clean PR branch.

Screenshots / recordings

Not a UI change.

Checklist

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

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2. Add Fixes #<number> or Closes #<number> to this PR description

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