Write a first community theme tutorial

[argentquest]

Goal

Give a new contributor a short, end-to-end tutorial for creating, testing, and sharing a Path Protocol theme.

Acceptance criteria

• begin from a clean local checkout and npm ci
• explain account creation and cloning the read-only default theme
• cover creating or editing a level, including wall selection, movement, resizing, rotation, validation, saving, and playtesting
• explain media provenance, licenses, account quotas, and public publishing
• show the checks contributors should run before opening a pull request
• link the tutorial from README.md and the Theme Workshop designer help