[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/slash_command.rs

@@ -33,6 +33,7 @@ pub enum SlashCommand {
     Mention,
     Status,
     Mcp,
+    Apps,
     Logout,
     Quit,
     Exit,
@@ -69,6 +70,7 @@ impl SlashCommand {
             SlashCommand::ElevateSandbox => "set up elevated agent sandbox",
             SlashCommand::Experimental => "toggle experimental features",
             SlashCommand::Mcp => "list configured MCP tools",
+            SlashCommand::Apps => "manage apps",
             SlashCommand::Logout => "log out of Codex",
             SlashCommand::Rollout => "print the rollout file path",
             SlashCommand::TestApproval => "test approval request",
@@ -104,6 +106,7 @@ impl SlashCommand {
             | SlashCommand::Status
             | SlashCommand::Ps
             | SlashCommand::Mcp
+            | SlashCommand::Apps
             | SlashCommand::Feedback
             | SlashCommand::Quit
             | SlashCommand::Exit => true,