Add startup rule to track and report new session start time

AGENTS.md

@@ -14,6 +14,7 @@ Before doing anything else:
 2. Read `USER.md` — this is who you're helping
 3. Read `memory/YYYY-MM-DD.md` (today + yesterday) for recent context
 4. **If in MAIN SESSION** (direct chat with your human): Also read `MEMORY.md`
+5. Record the new session start time at startup and keep it available to report to the user on request
 
 Don't ask permission. Just do it.
 

USER.md

@@ -4,7 +4,7 @@
 - **What to call them:** Fang
 - **Pronouns:** (unknown)
 - **Timezone:** Asia/Tokyo
-- **Notes:** Prefers task plans before execution, wants alternative options considered
+- **Notes:** Prefers task plans before execution, wants alternative options considered; on every new session, record the session start time and be ready to report it
 
 ## Context