Plugins TUI install/uninstall (#15342)

- Add install/uninstall actions to the TUI plugins menu
- Wire plugin install/uninstall through both TUI and `tui_app_server`
- Refresh config/plugin state after changes so the UI updates
immediately
- Add a post-install app setup flow for plugins that require additional
app auth

<img width="1567" height="300" alt="Screenshot 2026-03-20 at 4 08 44 PM"
src="https://github.com/user-attachments/assets/366bd31b-2ffd-4e80-b4a3-3a9a9c674a5f"
/>
<img width="445" height="240" alt="Screenshot 2026-03-20 at 4 08 54 PM"
src="https://github.com/user-attachments/assets/613999ab-269a-4758-ab59-7c057a1742dc"
/>
<img width="797" height="219" alt="Screenshot 2026-03-20 at 4 09 07 PM"
src="https://github.com/user-attachments/assets/b9679e60-40f5-49bb-ade0-2e40449c3fbf"
/>
<img width="499" height="235" alt="Screenshot 2026-03-20 at 4 09 24 PM"
src="https://github.com/user-attachments/assets/261ce2fe-f356-4e99-8ac9-f29ed850bc75"
/>




Note/known issue: The /plugin install flow fails in `tui_app_server`
because after a successful install it tries to trigger a
ReloadUserConfig operation, but `tui_app_server` has not yet implemented
transport for that operation, so it falls through to the generic “Not
available in app-server TUI yet” stub.

codex-rs/tui/src/app_event.rs

@@ -10,15 +10,18 @@
 
 use std::path::PathBuf;
 
+use codex_app_server_protocol::PluginInstallResponse;
 use codex_app_server_protocol::PluginListResponse;
 use codex_app_server_protocol::PluginReadParams;
 use codex_app_server_protocol::PluginReadResponse;
+use codex_app_server_protocol::PluginUninstallResponse;
 use codex_chatgpt::connectors::AppInfo;
 use codex_file_search::FileMatch;
 use codex_protocol::ThreadId;
 use codex_protocol::openai_models::ModelPreset;
 use codex_protocol::protocol::Event;
 use codex_protocol::protocol::RateLimitSnapshot;
+use codex_utils_absolute_path::AbsolutePathBuf;
 use codex_utils_approval_presets::ApprovalPreset;
 
 use crate::bottom_pane::ApprovalRequest;
@@ -193,6 +196,56 @@ pub(crate) enum AppEvent {
         result: Result<PluginReadResponse, String>,
     },
 
+    /// Replace the plugins popup with an install loading state.
+    OpenPluginInstallLoading {
+        plugin_display_name: String,
+    },
+
+    /// Replace the plugins popup with an uninstall loading state.
+    OpenPluginUninstallLoading {
+        plugin_display_name: String,
+    },
+
+    /// Install a specific plugin from a marketplace.
+    FetchPluginInstall {
+        cwd: PathBuf,
+        marketplace_path: AbsolutePathBuf,
+        plugin_name: String,
+        plugin_display_name: String,
+    },
+
+    /// Result of installing a plugin.
+    PluginInstallLoaded {
+        cwd: PathBuf,
+        marketplace_path: AbsolutePathBuf,
+        plugin_name: String,
+        plugin_display_name: String,
+        result: Result<PluginInstallResponse, String>,
+    },
+
+    /// Uninstall a specific plugin by canonical plugin id.
+    FetchPluginUninstall {
+        cwd: PathBuf,
+        plugin_id: String,
+        plugin_display_name: String,
+    },
+
+    /// Result of uninstalling a plugin.
+    PluginUninstallLoaded {
+        cwd: PathBuf,
+        plugin_id: String,
+        plugin_display_name: String,
+        result: Result<PluginUninstallResponse, String>,
+    },
+
+    /// Advance the post-install plugin app-auth flow.
+    PluginInstallAuthAdvance {
+        refresh_connectors: bool,
+    },
+
+    /// Abandon the post-install plugin app-auth flow.
+    PluginInstallAuthAbandon,
+
     InsertHistoryCell(Box<dyn HistoryCell>),
 
     /// Apply rollback semantics to local transcript cells.