feat(orchestration): add bttask CLI + GroupAgentsPanel + btmsg Tauri bridge
Phase 2: bttask CLI (Python, SQLite) — task management with role-based
visibility. Kanban board view. Manager/Architect can create tasks,
Tier 2 agents receive tasks via btmsg only.
Phase 3: GroupAgentConfig in groups.json + Rust backend. GroupAgentsPanel
Svelte component above ProjectGrid with status dots, role icons,
unread badges, start/stop buttons.
Phase 4: btmsg Rust bridge (btmsg.rs) — read/write access to btmsg.db.
6 Tauri commands for agent status, messages, and history.
GroupAgentsPanel polls btmsg.db every 5s for live status updates.
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