review: address ds-review-bot findings on session-stats

- stateVersion starts at 1: the package is new, no persisted rows predate it
- pendingCalls pairs by own key so a provider callId naming a prototype
  property cannot fold toolMs to NaN on an unmatched crash-recovery result
- StatsLine folds the window fallback only when no sessionStats value is
  served, and gates the token group on actual token activity instead of
  steps, so failed-only sessions drop the zero-token group
- correct the crash-step counting semantics in the README and Agent Note:
  recovery closes interrupted steps with a synthetic step/end on reload
- reword the window-scoped alternative as a plain rejected option and name
  isTokenDelta's home beside the StreamChunk type

packages/client/runtime/src/client/sessions/assistant-timing.ts

@@ -6,7 +6,7 @@ import { isTokenDelta } from '@deepseek-ai/dsh-llm/message'
 import type { SessionEvent } from '@deepseek-ai/dsh-session/types'
 import type { AssistantTiming } from './conversation.ts'
 
-// The first-token predicate lives with the StreamChunk vocabulary in dsh-llm;
+// The first-token predicate lives beside the StreamChunk type in dsh-llm;
 // re-exported here so Chat Definitions keep their client-runtime import.
 export { isTokenDelta } from '@deepseek-ai/dsh-llm/message'