fix: OpenCode Desktop compatibility - workspace changes shown across all sessions

[athal7]

• When using the plugin with OpenCode Desktop, all workspace changes are displayed for every conversation/session
• Expected behavior: each session should only see changes relevant to its own workspace context
• This may be related to how session state or workspace filtering is handled in the Desktop environment

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Resolution: This is an upstream OpenCode limitation. Instance.directory is set once at startup and doesn't update when switching workspaces mid-session.

Upstream issue: anomalyco/opencode#6697

Documented as known issue in README: d54202a