[connectors] Support connectors part 2 - slash command and tui (#9728)

- [x] Support `/apps` slash command to browse the apps in tui.
- [x] Support inserting apps to prompt using `$`.
- [x] Lots of simplification/renaming from connectors to apps.

codex-rs/tui/src/chatwidget/tests.rs

@@ -355,6 +355,7 @@ async fn interrupted_turn_restores_queued_messages_with_images_and_elements() {
             path: first_images[0].clone(),
         }],
         text_elements: first_elements,
+        mention_paths: HashMap::new(),
     });
     chat.queued_user_messages.push_back(UserMessage {
         text: second_text,
@@ -363,6 +364,7 @@ async fn interrupted_turn_restores_queued_messages_with_images_and_elements() {
             path: second_images[0].clone(),
         }],
         text_elements: second_elements,
+        mention_paths: HashMap::new(),
     });
     chat.refresh_queued_user_messages();
 
@@ -442,6 +444,7 @@ async fn remap_placeholders_uses_attachment_labels() {
         text,
         text_elements: elements,
         local_images: attachments,
+        mention_paths: HashMap::new(),
     };
     let mut next_label = 3usize;
     let remapped = remap_placeholders_for_message(message, &mut next_label);
@@ -502,6 +505,7 @@ async fn remap_placeholders_uses_byte_ranges_when_placeholder_missing() {
         text,
         text_elements: elements,
         local_images: attachments,
+        mention_paths: HashMap::new(),
     };
     let mut next_label = 3usize;
     let remapped = remap_placeholders_for_message(message, &mut next_label);
@@ -810,6 +814,7 @@ async fn make_chatwidget_manual(
         unified_exec_processes: Vec::new(),
         agent_turn_running: false,
         mcp_startup_status: None,
+        connectors_cache: ConnectorsCacheState::default(),
         interrupts: InterruptManager::new(),
         reasoning_buffer: String::new(),
         full_reasoning_buffer: String::new(),