[Feature Request] Document respectGitignore and fileSuggestion settings with UI feedback for filtered files

Bug Description
respectGitignore and fileSuggestion settings are undocumented. The @-mention file picker silently skips files listed in .gitignore by default (e.g. a gitignored CLAUDE.md), which is confusing — there's no visible indication of why a file doesn't appear. It took reverse-engineering the CLI binary to discover the respectGitignore: false top-level setting (in settings.json) that controls this, and the exact stdin/stdout contract for a custom fileSuggestion command ({"type":"command","command":"..."}, query passed as JSON on stdin, file paths expected newline-separated on stdout, 15-result cap, 5s timeout). Please document both in the official settings reference, and consider a subtle UI hint (e.g. "N files hidden by .gitignore") when the picker filters results.

Environment Info

• Platform: linux
• Terminal: guake
• Version: 2.1.207
• Feedback ID: d5e12d0b-4798-4bb4-b1af-0082ab98161d

Errors

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