feat(orchestration): multi-agent communication, unified agents, env passthrough

- btmsg: admin role (tier 0), channel messaging (create/list/send/history),
  admin global feed, mark-read conversations
- Rust btmsg module: admin bypass, channels, feed, 8 new Tauri commands
- CommsTab: sidebar chat interface with activity feed, DMs, channels (Ctrl+M)
- Agent unification: Tier 1 agents rendered as ProjectBoxes via agentToProject()
  converter, getAllWorkItems() combines agents + projects in ProjectGrid
- GroupAgentsPanel: click-to-navigate agents to their ProjectBox
- Agent system prompts: generateAgentPrompt() builds comprehensive introductory
  context (role, environment, team, btmsg/bttask docs, workflow instructions)
- AgentSession passes group context to prompt generator via $derived.by()
- BTMSG_AGENT_ID env var passthrough: extra_env field flows through full chain
  (agent-bridge → Rust AgentQueryOptions → NDJSON → sidecar runners → cleanEnv)
- workspace store: updateAgent() for Tier 1 agent config persistence

v2/src-tauri/src/lib.rs

@@ -131,6 +131,14 @@ pub fn run() {
             commands::btmsg::btmsg_history,
             commands::btmsg::btmsg_send,
             commands::btmsg::btmsg_set_status,
+            commands::btmsg::btmsg_ensure_admin,
+            commands::btmsg::btmsg_all_feed,
+            commands::btmsg::btmsg_mark_read,
+            commands::btmsg::btmsg_get_channels,
+            commands::btmsg::btmsg_channel_messages,
+            commands::btmsg::btmsg_channel_send,
+            commands::btmsg::btmsg_create_channel,
+            commands::btmsg::btmsg_add_channel_member,
             // Misc
             commands::misc::cli_get_group,
             commands::misc::open_url,