* refactor(installer): remove custom content installation feature
Remove the entire local filesystem custom content feature from the
installer to make way for marketplace-based plugin installation.
Deleted: custom-handler.js, custom-module-cache.js, custom-modules.js
Removed: --custom-content CLI flag, interactive custom content prompts,
custom module caching, manifest tracking, missing-source resolution,
and related test suites. Updated docs across all translations.
* fix: address review findings from Augment
Fix admonition syntax (remove accidental space in :::note) across 4
translated docs files, and update stale JSDoc on listAvailable().
5dbfb588ee