FlashFS 1.0.1

Release tooling and process documentation

- Add bump-version.sh: derives the ROM version from a tag's MAJOR.MINOR (patch ignored) and rewrites flash-fs.6502
- AGENTS.md: release procedure now requires the version bump to be committed and pushed before the tag
- No ROM code changes; ROM version stays 1.00 (1.0.x shares major.minor)