feat: theme refactoring

[atinux]

• Remove the hack around srcDir, this allow user to keep normal aliases and avoid dirty trick around them
• Use the module to inject the theme pages and layouts
• Remove the store/ to inject $docus instead and parallelise requests
• I dropped support for fetching the default branch

Closes #52 and resolves #51

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[atinux]

I need to handle the state injected from SSR