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).

src/store/chats.ts

@@ -14,7 +14,7 @@ import { emit } from "../core/events.ts";
 import type { ChatStore } from "../core/ports.ts";
 import type { ChatRecord, ChatSettings, ChatSummary, ExtractionRunUsage, PlanTree, TurnUsage } from "../core/contracts.ts";
 import type { LhMessage } from "../core/native-messages.ts";
-import { danglingQuestionOf } from "../core/native-messages.ts";
+import { activeProblemOf, danglingQuestionOf } from "../core/native-messages.ts";
 import { phaseAt3Lh } from "../core/phases.ts";
 
 function chatFile(id: string): string {