fix(web): stabilize canonical conversation terminal handling

[AgentArcLab]

Summary

• wait for explicit run-terminal events instead of treating completed items as completed runs
• preserve thinking/tool/approval/feedback presentation across streaming and replay
• replace the inert Pages placeholder with an interactive local demo covering incremental output, approval above the composer, and feedback
• prepare @kingsoftcloud/ksadk-web@0.3.4 release provenance and workflows

Verification

• npm run release:preflight
• 275 Vitest tests
• 120 Node contract tests
• canonical conversation Playwright scenarios
• interactive demo Playwright scenario
• independent npm pack install check

Consumer impact

This patch is intended for both AgentEngine Hosted UI and KsADK Studio static UI. The same published npm artifact must be used to rebuild both consumers. Formal npm publish and production deployment remain maintainer-gated.