### Changed
- File suggestions in chat input (`@` autocomplete) now respect `.gitignore` and `.ignore` rules from the workspace root. Files matching gitignore patterns are filtered out of search results, while negation patterns in `.ignore` (e.g., `!important.log`) can re-include previously ignored files. Ignore rules are cached for 30 seconds for performance. The file panel and file preview are unaffected — only `@` autocomplete suggestions use the new filtering.

### Added
- `ignore` package dependency for parsing `.gitignore`/`.ignore` files with full negation pattern support.
- `buildIgnoreFilter()` utility in `services/files.ts` that layers hardcoded ignore patterns, `.gitignore`, and `.ignore` rules in order, supporting negation overrides.
