Add support for global custom tools

[cte]

Important

Adds support for loading custom tools from multiple directories, including global directories, with UI and test updates.

• Behavior:
  • CustomToolRegistry now supports loading tools from multiple directories with loadFromDirectories() and loadFromDirectoriesIfStale().
  • Tools can be overridden by later directories in the list.
  • Handles non-existent directories and empty directory arrays gracefully.
• UI:
  • Updates CustomToolsSettings.tsx to display tool source paths.
  • Adds translations for new functionality in multiple language files.
• Tests:
  • Adds tests in custom-tool-registry.spec.ts for loading tools from multiple directories and handling stale directories.
• Misc:
  • Adds StoredCustomTool type in types.ts to include source information.
  • Updates build-tools.ts and webviewMessageHandler.ts to use new directory loading functions.

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[roomote]

Rooviewer   See task on Roo Cloud

Reviewed all changes since last review (f6429c7). No issues found.

The commit updates test snapshots to include the new source field for custom tools. The source: undefined entries reflect that test fixtures don't specify source paths.

Previous reviews

• 75c7ccf: Review #1
• 148e6e5: Review #2
• 023ed74: Review #3

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