P134 - Aux load prefetch policy

P134 is the pivot back to frontend/memory work after the P133 dispatch module proof. The backend queue boundary is coherent, but still one-deep and shadow-only. The memory counters still had a disabled aux-load path, so that is where this rung went.

The shell workload passed:

P134-FILE-OK @ cycle 218,247,710
post-load cycles  : 218,247,567
shell window      : 64,221,642
instr retired     : 86,139,760
CPI               : 2.5336

Aux-load policy result:

candidates             : 5,372,186
issues                 : 139,881
queue enqueues/dequeues: 139,881 / 139,881
queue full drops       : 0
aux load fills         : 139,881
aux errors/cancels     : 0 / 0

Compared with P133, shell-window time fell by 360,275 cycles. That is a small but real win, and more satisfying than another backend shadow counter.