* feat(installer): add community module browser and custom URL support
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
* fix: resolve review findings for community/custom module support
- Remove redundant CommunityModuleManager instantiation in UI display
- Remove dead customModulesMeta field from Config (never populated)
- Add 35 unit tests for CustomModuleManager and CommunityModuleManager
pure functions: URL validation, normalization, search, featured, categories
* fix: preserve installed community/custom modules in modify flow
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.
* fix: include community and custom modules in quick update
Quick update now checks community registry and custom cache so installed
community/custom modules are updated instead of skipped.
* fix: use defaults for new config fields during quick update
When quick update encounters new config fields (e.g., from a newly
supported community module), use schema defaults silently instead of
prompting the user. Quick update should be non-interactive.
* test: add unit tests for SHA pinning, category filtering, and URL edge cases
Cover SHA normalization (set vs null/trusted), listByCategory,
getModuleByCode, and URL validation edge cases (HTTP, trailing slash,
SSH without .git). Total: 243 tests.
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