fix(context): use agent ID not name for GetAgentFile fallback lookup

cb.agentID was set to a.name (display name like "拽姐") instead of
a.agentID (database ID like "agt_xxx"). The GetAgentFile fallback
subquery `SELECT user_id FROM agents WHERE id = ?` failed silently,
so SOUL.md/IDENTITY.md were missing from the system prompt when the
UserSpace owner differs from the agent owner (e.g. app_user channels).

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

Author: idoubi

internal/agent/loop.go

@@ -3288,7 +3288,7 @@ func (a *Agent) ReloadWorkspaceFiles() {
 	// name/soul" greeting).
 	if a.memoryStore != nil {
 		a.ctxBuilder.store = a.memoryStore
-		a.ctxBuilder.agentID = a.name
+		a.ctxBuilder.agentID = a.agentID
 		a.ctxBuilder.userID = a.ownerUserID
 	}
 	// Chatter-timezone date line — same re-apply rule as the Store