- Add shared threadTerminalState.ts: ThreadTerminalState type, default state,
  normalize helpers, and single reduceThreadTerminalState() used by both flows
- Refactor store.ts to use shared terminal reducer and helpers; terminal
  actions map to reduceThreadTerminalState(threadTerminalSlice(thread), action)
- Make draftThreadTerminalState.ts re-export shared module (same shape/actions)
- Add terminalState to composer draft store: getDraftThreadTerminalState,
  setDraftThreadTerminalAction, clearDraftThreadTerminalState; draft thread
  shape matches Thread terminal slice
- ChatView: move draft terminal from useState into composer draft store; use
  same actions for draft and persisted; hydrate then clear draft terminal
  when reconciling server state

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