Fully support all mention kinds (#36134)

Feature parity with the agent1 @mention kinds:
- File
- Symbols
- Selections
- Threads
- Rules
- Fetch


Release Notes:

- N/A

---------

Co-authored-by: Cole Miller <cole@zed.dev>

crates/agent_ui/src/agent_panel.rs

@@ -973,6 +973,9 @@ impl AgentPanel {
             agent: crate::ExternalAgent,
         }
 
+        let thread_store = self.thread_store.clone();
+        let text_thread_store = self.context_store.clone();
+
         cx.spawn_in(window, async move |this, cx| {
             let server: Rc<dyn AgentServer> = match agent_choice {
                 Some(agent) => {
@@ -1011,6 +1014,8 @@ impl AgentPanel {
                         server,
                         workspace.clone(),
                         project,
+                        thread_store.clone(),
+                        text_thread_store.clone(),
                         message_history,
                         MIN_EDITOR_LINES,
                         Some(MAX_EDITOR_LINES),