docs: document fasmg syntax validation workflow

[sit-d]

Summary

• update test_suit/README.md now that scripts/validate.py exists
• document the low-cost Python syntax check and generator/linter command for contributors
• regenerate the Notepad++ UDL output so dist/fasmg.udl.xml matches the current generator's XML escaping

Verification

• python3 -m py_compile scripts/*.py
• python3 scripts/gen_all.py --lint → lint: all 46 regex patterns OK in fasmg.tmLanguage.json
• python3 - <<'PY' ... ET.parse('dist/fasmg.udl.xml') ... PY → XML parse OK

Notes / Limitations

• Full fixture assembly validation was not run in this Linux cron environment because scripts/validate.py could not locate a fasmg executable: error: could not locate fasmg. Pass --fasmg PATH_TO_FASMG or add it to PATH.