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/lib/adapters/btmsg-bridge.ts

@@ -29,6 +29,38 @@ export interface BtmsgMessage {
   sender_role?: string;
 }
 
+export interface BtmsgFeedMessage {
+  id: string;
+  fromAgent: string;
+  toAgent: string;
+  content: string;
+  createdAt: string;
+  replyTo: string | null;
+  senderName: string;
+  senderRole: string;
+  recipientName: string;
+  recipientRole: string;
+}
+
+export interface BtmsgChannel {
+  id: string;
+  name: string;
+  groupId: string;
+  createdBy: string;
+  memberCount: number;
+  createdAt: string;
+}
+
+export interface BtmsgChannelMessage {
+  id: string;
+  channelId: string;
+  fromAgent: string;
+  content: string;
+  createdAt: string;
+  senderName: string;
+  senderRole: string;
+}
+
 /**
  * Get all agents in a group with their unread counts.
  */
@@ -70,3 +102,59 @@ export async function sendMessage(fromAgent: string, toAgent: string, content: s
 export async function setAgentStatus(agentId: string, status: string): Promise<void> {
   return invoke('btmsg_set_status', { agentId, status });
 }
+
+/**
+ * Ensure admin agent exists with contacts to all agents.
+ */
+export async function ensureAdmin(groupId: string): Promise<void> {
+  return invoke('btmsg_ensure_admin', { groupId });
+}
+
+/**
+ * Get all messages in group (admin global feed).
+ */
+export async function getAllFeed(groupId: string, limit: number = 100): Promise<BtmsgFeedMessage[]> {
+  return invoke('btmsg_all_feed', { groupId, limit });
+}
+
+/**
+ * Mark all messages from sender to reader as read.
+ */
+export async function markRead(readerId: string, senderId: string): Promise<void> {
+  return invoke('btmsg_mark_read', { readerId, senderId });
+}
+
+/**
+ * Get channels in a group.
+ */
+export async function getChannels(groupId: string): Promise<BtmsgChannel[]> {
+  return invoke('btmsg_get_channels', { groupId });
+}
+
+/**
+ * Get messages in a channel.
+ */
+export async function getChannelMessages(channelId: string, limit: number = 100): Promise<BtmsgChannelMessage[]> {
+  return invoke('btmsg_channel_messages', { channelId, limit });
+}
+
+/**
+ * Send a message to a channel.
+ */
+export async function sendChannelMessage(channelId: string, fromAgent: string, content: string): Promise<string> {
+  return invoke('btmsg_channel_send', { channelId, fromAgent, content });
+}
+
+/**
+ * Create a new channel.
+ */
+export async function createChannel(name: string, groupId: string, createdBy: string): Promise<string> {
+  return invoke('btmsg_create_channel', { name, groupId, createdBy });
+}
+
+/**
+ * Add a member to a channel.
+ */
+export async function addChannelMember(channelId: string, agentId: string): Promise<void> {
+  return invoke('btmsg_add_channel_member', { channelId, agentId });
+}