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/commands/btmsg.rs

@@ -29,3 +29,43 @@ pub fn btmsg_send(from_agent: String, to_agent: String, content: String) -> Resu
 pub fn btmsg_set_status(agent_id: String, status: String) -> Result<(), String> {
     btmsg::set_status(&agent_id, &status)
 }
+
+#[tauri::command]
+pub fn btmsg_ensure_admin(group_id: String) -> Result<(), String> {
+    btmsg::ensure_admin(&group_id)
+}
+
+#[tauri::command]
+pub fn btmsg_all_feed(group_id: String, limit: i32) -> Result<Vec<btmsg::BtmsgFeedMessage>, String> {
+    btmsg::all_feed(&group_id, limit)
+}
+
+#[tauri::command]
+pub fn btmsg_mark_read(reader_id: String, sender_id: String) -> Result<(), String> {
+    btmsg::mark_read_conversation(&reader_id, &sender_id)
+}
+
+#[tauri::command]
+pub fn btmsg_get_channels(group_id: String) -> Result<Vec<btmsg::BtmsgChannel>, String> {
+    btmsg::get_channels(&group_id)
+}
+
+#[tauri::command]
+pub fn btmsg_channel_messages(channel_id: String, limit: i32) -> Result<Vec<btmsg::BtmsgChannelMessage>, String> {
+    btmsg::get_channel_messages(&channel_id, limit)
+}
+
+#[tauri::command]
+pub fn btmsg_channel_send(channel_id: String, from_agent: String, content: String) -> Result<String, String> {
+    btmsg::send_channel_message(&channel_id, &from_agent, &content)
+}
+
+#[tauri::command]
+pub fn btmsg_create_channel(name: String, group_id: String, created_by: String) -> Result<String, String> {
+    btmsg::create_channel(&name, &group_id, &created_by)
+}
+
+#[tauri::command]
+pub fn btmsg_add_channel_member(channel_id: String, agent_id: String) -> Result<(), String> {
+    btmsg::add_channel_member(&channel_id, &agent_id)
+}