Add FF + base components for file tree browser
What does this MR do and why?
Adds a feature flag and initial components (without list of files) for the repository tree browser component.
Implementation Breakdown:
- 
Terminology:
- *Existing file tree (list of files) → File tree
 - *New file tree browser component → File tree browser (FTB)
 
 
| Task | Status | Notes | 
|---|---|---|
| Add FF + base components for file tree browser (FTB) | 
 | 
|
| Render a basic FTB + files next to the file tree | follow-up MR/issue | |
| Render a basic FTB + files next to the blob viewer | follow-up MR/issue | |
| Navigate from file tree → blob via FTB without refresh | follow-up MR/issue | |
| Navigate from file tree → tree via FTB without refresh | follow-up MR/issue | |
| Navigate from blob → file tree vis FTB without refresh | follow-up MR/issue | Requires passing extra props for tree to render | 
| Navigate from overview → file tree/blob without refresh | follow-up MR/issue | FTB should not render on overview page | 
| Share state between FTB and file tree | follow-up MR/issue | |
| Indicate the current file in the FTB | follow-up MR/issue | |
| Implement file browser panel resizer | follow-up MR/issue | |
| Implement expand/collapse toggle + auto-collapse on mobile | follow-up MR/issue | |
| Implement filtering | follow-up MR/issue | |
| Match the styling of MR file browser + responsiveness | follow-up MR/issue | |
| Implement ARIA tree view pattern | follow-up MR/issue | See #525169 (comment 2447409353) | 
Screenshots or screen recordings
| Before | After | 
|---|---|
![]()  | 
![]()  | 
![]()  | 
![]()  | 
How to set up and validate locally
- Enable the 
repository_file_tree_browserflag - Navigate to either the repository blob viewer or tree list (not project overview)
 - The file tree browser should render
 
Related to #536028 (closed)
Edited  by Jacques Erasmus



