feat: add Matrix coordination channel, replace openclaw (Closes #8)

Add matrix_send() to lib/env.sh and matrix_listener.sh daemon for
real-time notifications, threaded escalations, and human-in-the-loop
replies. All agents now notify via Matrix instead of openclaw.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

dev/dev-agent.sh

@@ -55,7 +55,7 @@ status() {
 }
 
 notify() {
-  openclaw system event --text "🔧 dev-agent #${ISSUE}: $*" --mode now 2>/dev/null || true
+  matrix_send "dev" "🔧 #${ISSUE}: $*" 2>/dev/null || true
 }
 
 cleanup_worktree() {