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/scripts/get_developer.py

@@ -0,0 +1,26 @@
+#!/usr/bin/env python3
+"""
+Get current developer name.
+
+This is a wrapper that uses common/paths.py
+"""
+
+from __future__ import annotations
+
+import sys
+
+from common.paths import get_developer
+
+
+def main() -> None:
+    """CLI entry point."""
+    developer = get_developer()
+    if developer:
+        print(developer)
+    else:
+        print("Developer not initialized", file=sys.stderr)
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()