[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/app-server-protocol/src/protocol/v2.rs

@@ -1003,6 +1003,8 @@ pub struct AppInfo {
     pub name: String,
     pub description: Option<String>,
     pub logo_url: Option<String>,
+    pub logo_url_dark: Option<String>,
+    pub distribution_channel: Option<String>,
     pub install_url: Option<String>,
     #[serde(default)]
     pub is_accessible: bool,
@@ -1897,6 +1899,10 @@ pub enum UserInput {
         name: String,
         path: PathBuf,
     },
+    Mention {
+        name: String,
+        path: String,
+    },
 }
 
 impl UserInput {
@@ -1912,6 +1918,7 @@ impl UserInput {
             UserInput::Image { url } => CoreUserInput::Image { image_url: url },
             UserInput::LocalImage { path } => CoreUserInput::LocalImage { path },
             UserInput::Skill { name, path } => CoreUserInput::Skill { name, path },
+            UserInput::Mention { name, path } => CoreUserInput::Mention { name, path },
         }
     }
 }
@@ -1929,6 +1936,7 @@ impl From<CoreUserInput> for UserInput {
             CoreUserInput::Image { image_url } => UserInput::Image { url: image_url },
             CoreUserInput::LocalImage { path } => UserInput::LocalImage { path },
             CoreUserInput::Skill { name, path } => UserInput::Skill { name, path },
+            CoreUserInput::Mention { name, path } => UserInput::Mention { name, path },
             _ => unreachable!("unsupported user input variant"),
         }
     }
@@ -2732,6 +2740,10 @@ mod tests {
                     name: "skill-creator".to_string(),
                     path: PathBuf::from("/repo/.codex/skills/skill-creator/SKILL.md"),
                 },
+                CoreUserInput::Mention {
+                    name: "Demo App".to_string(),
+                    path: "app://demo-app".to_string(),
+                },
             ],
         });
 
@@ -2754,6 +2766,10 @@ mod tests {
                         name: "skill-creator".to_string(),
                         path: PathBuf::from("/repo/.codex/skills/skill-creator/SKILL.md"),
                     },
+                    UserInput::Mention {
+                        name: "Demo App".to_string(),
+                        path: "app://demo-app".to_string(),
+                    },
                 ],
             }
         );