raidboss: initial r12s p1 triggers and timeline (#1002)

Breaking apart p1 from p2 in #964.

Some ideas of TODOs for P1:
- Find safe spots for Curtain Call Unbreakable Flesh
- Find safe spots for Slaughtershed Stack/Spreads

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Co-authored-by: Dowon <ks2515@naver.com>

Author: Legends0