Improve MegaBirthShpTail2 frame local lifetimes

[asmithbot]

Summary

• Hoists particle loop locals in pppFrameYmMegaBirthShpTail2 so their lifetimes better match the original function
• Keeps the generated code size stable while improving register allocation in the frame loop

Evidence

• ninja passes
• objdiff main/pppYmMegaBirthShpTail2 .text: 54.366684% -> 54.54793% (size 7636 unchanged)
• objdiff pppFrameYmMegaBirthShpTail2: 97.48881% -> 98.779854% (size 1072 unchanged)

Plausibility

• This is source-level local lifetime cleanup only; no hardcoded addresses, fake symbols, section forcing, or generated ctor/dtor hacks.

[decomp-dev]

Report for GCCP01 (8d93249 - 0a983d8)

📈 1 improvement in an unmatched item

Unit	Item	Bytes	Before	After
main/pppYmMegaBirthShpTail2	pppFrameYmMegaBirthShpTail2	+12	97.49%	98.65%