Add workspace index and developer-specific journals for AI sessions

- Created a main workspace index to track AI Agent work records across developers.
- Added a personal index for developer 'yuxuanhui' with current status and session history.
- Initialized the first journal file for 'yuxuanhui' to document AI development sessions.
- Introduced AGENTS.md for Trellis instructions, detailing project structure and usage guidelines.

.trellis/spec/backend/logging-guidelines.md

@@ -0,0 +1,51 @@
+# Logging Guidelines
+
+> How logging is done in this project.
+
+---
+
+## Overview
+
+<!--
+Document your project's logging conventions here.
+
+Questions to answer:
+- What logging library do you use?
+- What are the log levels and when to use each?
+- What should be logged?
+- What should NOT be logged (PII, secrets)?
+-->
+
+(To be filled by the team)
+
+---
+
+## Log Levels
+
+<!-- When to use each level: debug, info, warn, error -->
+
+(To be filled by the team)
+
+---
+
+## Structured Logging
+
+<!-- Log format, required fields -->
+
+(To be filled by the team)
+
+---
+
+## What to Log
+
+<!-- Important events to log -->
+
+(To be filled by the team)
+
+---
+
+## What NOT to Log
+
+<!-- Sensitive data, PII, secrets -->
+
+(To be filled by the team)