fix(streaming): stabilize thinking block identity

[Kaguya-19]

Summary

• add stable thinkingBlockId/thinkingBlockSeq through canonical, gateway, bridge, and web protocol
• normalize provider thinking deltas to one live block identity and keep legacy fallback when fields are missing
• update live UI/store replay/finalization to merge by block key without touching history refresh paths

Tests

• npx tsc -p tsconfig.json --noEmit
• PATH=/Users/a1/.nvm/versions/node/v22.23.1/bin:$PATH npm run build
• npx tsx --test tests/model/streaming/thinkingBlockIdentity.spec.ts tests/web/thinking-block.spec.ts tests/gateway/map-agent-event-runid.spec.ts
• npm --prefix ui test -- useSessionStore.streaming.test.ts pilotdeck-bridge.test.js