[SultanGun]

Summary

Prevent ignored files from being accessed through alternate casing on case-insensitive filesystems.

Problem

Ignore rules could be bypassed by changing the capitalization of a file or directory path on Windows and macOS. This could allow file tools to access files that should remain ignored.

Changes

• Add a shared platform policy for case-insensitive filesystem handling.
• Normalize ignore patterns and candidate paths consistently on Windows and macOS.
• Add matcher tests for filenames, directories, globs, negation, and Linux case-sensitive behavior.
• Add integration tests for FileReadTool, FileWriteTool, and FilePatchTool to prevent alternate-case bypasses.

Verification

• go test ./internal/ignore -v -count=1
• go test ./internal/tools -run "^TestTools_IgnoreRules" -v -count=1
• go vet ./...
• gofmt -l .
• Linux and macOS cross-compilation checks passed.

The full Windows tools test suite has known file-sharing violation failures in tests involving file writes. The affected write implementation is unchanged by this PR; the issue is being addressed separately.

Scope

This PR addresses ignore-rule enforcement only. It does not include the separate Windows file-sharing retry fix.