practice polish: no phantom wake, Practice header tag, honest meta

- needsContinuation: a persisted problem-pose ack (terminate:true ended
  the turn deliberately) owes no continuation — reloads after a pose no
  longer wake a phantom turn; error results stay owed like any
  interrupted tool.
- Chat header: practice sessions swap the phase chip for a quiet
  Practice tag (no probe→teach arc applies) and hide the coverage ring
  (practice never extracts — an ever-filling ring would lie).
- ChatSummary gains pendingProblem (activeProblemOf at projection); the
  sidebar meta says 'Problem waiting' for a practice row with a posed
  problem. Kind threads through Chat/[id] page.
- Home picker chip gains Clear (picks were otherwise irremovable).

components/sidebar.tsx

@@ -227,6 +227,9 @@ export function timeAgo(iso: string, now = new Date()): string {
  *  ever wanted. */
 function sessionMeta(chat: ChatListItem): string {
 	if (chat.pendingQuestion) return `Waiting for your answer · ${timeAgo(chat.updatedAt)}`;
+	if ((chat.kind ?? "teach") === "practice" && chat.pendingProblem) {
+		return `Problem waiting · ${timeAgo(chat.updatedAt)}`;
+	}
 	if (chat.busy) return (chat.kind ?? "teach") === "practice" ? "Practicing…" : "Teacher is working…";
 	return timeAgo(chat.updatedAt);
 }