When a user does "Modify Installation" and declines to browse community
modules, previously installed community/custom modules are now auto-kept.
If the user does browse, their selections are trusted (they can deselect).
Also fix stale docs: class doc for SHA pinning, JSDoc return type.
Three-tier module selection: official, community (category drill-down
with featured/search), and custom GitHub URL.
- Add RegistryClient shared fetch utility
- Add CommunityModuleManager with SHA-pinned cloning (refuses install
if approved SHA cannot be reached; uses HEAD when no SHA set)
- Add CustomModuleManager for arbitrary GitHub repo installation
- Extend findModuleSource chain with community and custom fallthrough
- Extend manifest to detect community and custom source types
- Add Config.customModulesMeta for custom module metadata
Brian Madison