Feat/updating filetree page ts - #142

Summary

• Rewrites the FileTree page in TypeScript and organizes it as an independent feature.
• Adds branch and snapshot selection, commit-only file scope, flat and tree grouping, search, selection, and path copying.
• Compares commit files with the selected snapshot's actual parent, including branch merge commits.
• Adds aggregated partition and partition-path statistics.
• Adds a resizable file information panel with consistent shared panel behavior and keyboard navigation.
• Handles historical branches, incomplete snapshot ranges, nullable backend values, and invalid graph data safely.

Closes #112
Closes #62