feat: optimize chat stream stability, security, and frontend rendering performance- Security: Added sensitive data redaction (masking password, secret, token, apiKey) for trace logs in backend utility request/response body parsing.

• Stability: Enhanced Durable Object state recovery by persisting and restoring runtime payloads, ensuring the process queue resumes on restart, and adding a 100-second upstream API fetch timeout.
• Database: Bumped DB schema version to 15, adding applySchemaV14 and applySchemaV15 compatibility stubs.
• Performance: Refactored ChatSession message lists by extracting and memoizing UserMessageRow and AssistantMessageRow with React.memo, and extracted static Markdown plugins outside of render scopes to eliminate redundant parsing.
• State Management: Integrated Zustand useShallow selectors across App, ChatInputArea, and ChatSession to prevent unnecessary re-renders.
• Resilience: Upgraded stream reconnect/resume flow in the store to pass existing stream progress (content and reasoning), preventing flickering and duplicate content rendering on stream recovery.