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/.gitignore

@@ -0,0 +1,32 @@
+# Developer identity (local only)
+.developer
+
+# Current task pointer (each dev works on different task)
+.current-task
+
+# Session/window scoped runtime state
+.runtime/
+
+# Ralph Loop state file
+.ralph-state.json
+
+# Agent runtime files
+.agents/
+.agent-log
+.session-id
+
+# Task directory runtime files
+.plan-log
+
+# Atomic update temp files
+*.tmp
+
+# Update backup directories
+.backup-*
+
+# Conflict resolution temp files
+*.new
+
+# Python cache
+**/__pycache__/
+**/*.pyc