v28062026: Add fizz skill (Echidna/Medusa fuzz suite generator) (#32)

* Add fizz skill (third tool alongside x-ray and solidity-auditor)

Vendors the Fizz skill (https://github.com/PashovAuditGroup/fizz) into the
monorepo following the x-ray/solidity-auditor convention:

- fizz/ — SKILL.md, README.md, VERSION (1), and the skill's agents/
  references/scripts/skills/templates/evals trees
- README.md uses the lean sibling style (## Demo with the GIF in the shared
  root static/, lean ## Usage); standalone clone+symlink install dropped
- static/fizz.gif added alongside x_ray.gif and skill_pag.gif
- Root README: fizz added to the Skills table (alphabetical) and to the
  install/run prompt blocks

Note: fizz/SKILL.md intentionally references x-ray — Fizz consumes x-ray's
output as a project-understanding input, so those references are kept as-is.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* fizz README: drop 'not a replacement' line per review

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: 0xfirefistt <0xfirefistt@users.noreply.github.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>