nx_riscv_emu.nx

nx_riscv_emu.nx -- SOVEREIGN RISC-V backend, RUNG 5: execute the ELF our writer emitted. Now on the GENERAL nx_riscv_lib (shared rv64im emulator `run`, ELF reader helpers, encoders) -- only the load + tests are local. T1 parse e_entry == 0x10078. T2 EXECUTE riscv_prog.elf -> exit 40 (5*8) = LOOP CLOSED. T3 (teeth) patch the two source immediates in memory (5->6, 8->7) -> exit 42 (6*7) = genuinely computes. expect_exit: 0 Sovereign: nx_riscv_lib (+ nx_syscalls). No qemu/gcc/objdump/sh.