test(btmsg): add regression tests for named column access and camelCase serialization

Covers the CRITICAL status vs system_prompt bug (positional index 7),
JOIN alias disambiguation, serde camelCase serialization, TypeScript
bridge IPC commands, and plantuml hex encoding algorithm.
49 new tests: 8 btmsg.rs + 7 bttask.rs + 8 sidecar + 17 btmsg-bridge.ts + 10 bttask-bridge.ts + 7 plantuml-encode.ts

v2/src-tauri/src/groups.rs

@@ -191,6 +191,7 @@ mod tests {
                     profile: "default".to_string(),
                     enabled: true,
                 }],
+                agents: vec![],
             }],
             active_group_id: "test".to_string(),
         };