Prepare ShadowPets for public reuse

[throwingogo-hub]

What changed

• clarifies the ShadowPets product identity and download path
• licenses artwork under CC BY 4.0 and code/docs under MIT
• adds copy-ready attribution and contribution guidance
• adds comprehensive non-mutating asset validation
• adds deterministic release packaging and tag-driven release automation
• adds a 1280×640 social preview plus page sharing metadata
• adds focused issue and pull request templates

Why

The art was polished but legally ambiguous and difficult to consume as a game-ready pack. This makes reuse, verification, packaging, and discovery explicit.

Verification

• 10 pets, 90 PNG frames, 30 GIFs, and 10 sheets validated
• shared 17-colour palette and hard alpha validated
• rebuild is byte-for-byte reproducible without tracked mutations
• release ZIP is deterministic and SHA-256 verified
• gallery browser QA passes with zero broken images, console errors, or overflow
• approved pet artwork is unchanged