* fix(opencode): default agent switching to disabled
* fix(opencode): keep plan-approval build handoff; default no-switch for review feedback only
The agent switch cookie is shared by plan approval and code review, so
flipping the stored default to `disabled` also removed OpenCode's
plan-approval hand-off for every user who never configured the setting.
Make the unset default surface-aware instead: `getAgentSwitchSettings('plan')`
keeps the historical build hand-off, `getAgentSwitchSettings('review')`
stays on the current agent. An explicit user choice still applies to both
surfaces. Settings and the agent warning resolve the default from the mode
they render in, and the OpenCode "agent not available" warning now names
plan approval on the plan path.
Claude-Session: https://claude.ai/code/session_01H5KQWqXqjrPxyxUNso1QHS
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Co-authored-by: Michael Ramos <mdramos8@gmail.com>
Brad Beebe