[FEATURE] fileSuggestion: support include list to surface gitignored paths in @ autocomplete

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

The @ file autocomplete respects .gitignore by default, which is correct for most files. However, there are common cases where specific folders (e.g. secrets/, local-config/) are gitignored but should still be discoverable via @ —
without disabling .gitignore entirely via respectGitignore: false.

The current workaround requires a custom fileSuggestion command script, which is non-trivial to set up.

Proposed Solution

Add a native include list to settings.json that exceptions specific paths from the gitignore filter:

{
"fileSuggestionInclude": ["secrets", "local-config"]
}

For project-level overrides, support a .claudeinclude file in the project root (one path per line), mirroring the .gitignore convention:

secrets/
local-config/

Both sources would merge, with project-level entries scoped to that project.

Alternative Solutions

#### Why not respectGitignore: false?

That disables gitignore entirely, flooding autocomplete with build artifacts, dependencies, and other noise. The ask is surgical: opt specific folders in, keep everything else filtered.

Priority

Medium - Would be very helpful

Feature Category

File operations

Use Case Example

_No response_

Additional Context

_No response_