fix(agents): restore archived tasks for continued conversation (#349)

Archived agent tasks could be opened but never returned to the active list, so their message composer stayed disabled. Unarchive is now available in the task header, in the archived-task notice above the composer, and in the task context menu (including mixed bulk selections). Restoring a task moves it back to the active list, keeps its conversation and worktree, and reconnects the existing agent session on the next message; the backend persists and broadcasts the restored status and refuses restoration while a stopped turn is still settling.

src/bindings.ts

@@ -112,6 +112,7 @@ export const commands = {
 	/**  Answers a permission request; `option: null` cancels it. */
 	agentRespond: (task: string, permission: number, option: string | null) => typedError<null, IdeError>(__TAURI_INVOKE("agent_respond", { task, permission, option })),
 	agentArchive: (task: string) => typedError<null, IdeError>(__TAURI_INVOKE("agent_archive", { task })),
+	agentUnarchive: (task: string) => typedError<null, IdeError>(__TAURI_INVOKE("agent_unarchive", { task })),
 	agentDelete: (task: string, removeWorktree: boolean) => typedError<null, IdeError>(__TAURI_INVOKE("agent_delete", { task, removeWorktree })),
 	agentChanges: (task: string) => typedError<AgentChange[], IdeError>(__TAURI_INVOKE("agent_changes", { task })),
 	/**  Content of `path` when the task started (left side of its diff). */