call and read implemented

The interactive primitives (D129). call <addr> <args> and read <addr> <len> added to the net.c server, announced as capabilities. Proven live on the host serve build: read returned the ELF magic from process memory, call returned a real function's value, and call 0x0 left a lone ack (the died signature) with the process gone.

Surprises

• Both live bugs were wrong-record, not crashes: a double 0x in the read id, and a null address refused instead of called (which hid the death path). The socket test caught both; neither showed up in the build.
• The shadPS4 serving path now dies after the newly-added 160-gpu section on that loader, before reaching listen - so call/read were proven on the host socket rather than in shadPS4 this round. Same net.c either way. The gpu-section crash on shadPS4 is a separate item.