Add POSIX fasm2 wrapper

[sit-d]

Summary

• add fasm2.sh, a POSIX counterpart to fasm2.cmd, that prepends the repo-local include directory and injects Include('fasm2.inc')
• document the Windows and POSIX wrapper entry points in the root README

Verification

• ./fasm2.sh -e 5 examples/globstr/demo_linux.asm /tmp/demo_linux
• file /tmp/demo_linux
• /tmp/demo_linux
• sh -n fasm2.sh
• git diff --check

The assembled Linux globstr demo ran and printed Hello, it's /tmp/demo_linux speaking.

Notes / limitations

• This does not change the existing Windows wrapper or example sources.
• I verified a Linux ELF example with the checked-in fasmg.x64; Windows examples were not rebuilt from this Linux cron environment.

[sit-d]

Ad-hoc verification rerun after wrapper cleanup:

• Created a temporary verifier under /tmp with a hermes-verify- prefix.
• The verifier set an existing bogus INCLUDE value, then ran ./fasm2.sh -e 5 examples/globstr/demo_linux.asm <temp-output> to confirm the wrapper prepends the repo include path correctly.
• Result: build exited 0, assembled in 3 passes, file identified the output as ELF64, executing the output printed the expected Hello... greeting, and sh -n fasm2.sh exited 0.
• The temporary verifier file was removed after the run.

This is ad-hoc verification, not a canonical suite result.