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).

tests/render-sidebar.test.tsx

@@ -27,6 +27,7 @@ function item(overrides: Partial<ChatListItem>): ChatListItem {
 		messageCount: 4,
 		phase: "probe",
 		pendingQuestion: false,
+		pendingProblem: false,
 		busy: false,
 		...overrides,
 	};
@@ -135,4 +136,9 @@ describe("SessionRow practice badge (practice sessions, 2026-10-04)", () => {
 		const html = render(item({ busy: true }));
 		assert.match(html, /Teacher is working…/);
 	});
+
+	it("a practice row with a posed problem says the problem is waiting", () => {
+		const html = render(item({ kind: "practice", pendingProblem: true }));
+		assert.match(html, /Problem waiting ·/);
+	});
 });