docs: add the PHB-24 theme page, list it in Themes
Restructure Wiki into a tutorial for module authors Rewrites the Wiki as a step-by-step tutorial + reference, replacing the previous dev-reference-style docs (moved to OLD/ during the transition). New structure: - Home: getting-started path + reference index - Create a Project, The Extension Panel - Creating Module Content (Pages, Groups, Maps and Encounters) - Managing the Compendium (Items, Spells, Roll Tables, Monsters) - Snippets, Themes (5.5e), Building and Importing - Project Settings, Advanced Settings (Commands) Includes screenshots throughout, taken against a sample module.