Add tree view option for Git panel to display changed files in directory structure

[AndreyZlobin]

Summary

Add an option to display changed files in the Git panel as a tree structure instead of only a flat list.

Current Behavior

The Git panel currently shows all changed files as a flat list, regardless of their location in the project structure. For projects with many changed files across different directories, this makes it difficult to:

• Understand which parts of the project are affected
• Navigate to related files in the same directory
• Get a quick overview of the scope of changes

Desired Behavior

Add a toggle option in the Git panel to switch between:

1. Flat view (current behavior) - all files in a single list
2. Tree view - files organized by their directory structure

Proposed Solution

Settings Option

"git_panel": {
  "file_display_mode": "tree" // or "flat"
}

UI Toggle

Add a button in the Git panel toolbar to switch between views on-the-fly (similar to how file icons can be toggled).

Visual Example

**Current (Flat):

Modified Files (12)
├─ src/components/Button.tsx
├─ src/components/Input.tsx
├─ src/utils/helpers.ts
├─ src/utils/validators.ts
├─ src/pages/Home.tsx
├─ src/pages/About.tsx
└─ ...

Proposed (Tree):

Modified Files (12)
└─ src/
   ├─ components/
   │  ├─ Button.tsx
   │  └─ Input.tsx
   ├─ utils/
   │  ├─ helpers.ts
   │  └─ validators.ts
   └─ pages/
      ├─ Home.tsx
      └─ About.tsx

Benefits

1. Better organization - Easier to understand which directories are affected by changes
2. Faster navigation - Related files are visually grouped together
3. Collapsible sections - Can collapse directories you're not currently interested in
4. Scalability - Works better for large changesets with files from many directories
5. Consistency - Matches the mental model from the project panel

Use Cases

• Large refactoring - When changing many files across different modules, tree view helps maintain context
• Feature development - When working on a feature that touches multiple files in specific directories
• Code review - Easier to review changes by directory/module
• Monorepo workflows - When working with multiple apps/packages, tree structure shows which packages are affected

Additional Features (Optional)

• Remember collapsed/expanded state of directories
• Show directory-level statistics (e.g., "5 files changed in this directory")
• Right-click on directory to stage/unstage all files in it
• Keyboard navigation similar to project panel

Additional Context

Tree view is especially valuable for:

• Monorepo projects with multiple applications
• Large codebases with deep directory structures
• Teams that organize code by feature/module in separate directories

[SomeoneToIgnore]

#35803