Implement: Full version control UI for ComfyUI core (commit timeline + checkout)

## Problem

Desktop users currently have limited version control capabilities when debugging workflow issues. When workflows break after ComfyUI updates, users need to test against different commits or stable releases to isolate the problem. Current snapshot functionality only works for already-installed versions, making it difficult to roll back to specific commits for debugging.

## Proposed Solution

Add full Git-like version control UI to Desktop, similar to what Huishi Launcher provides:

* Display a timeline of ComfyUI core commits
* Allow users to switch between different commits on demand
* Show stable releases and development versions clearly
* Enable checkout of specific commits for debugging purposes

This would significantly improve the debugging experience when workflows break, as users could easily bisect to find which commit introduced an issue.

## Reference Implementation

Huishi Launcher already implements this pattern successfully:


The interface shows:

* Commit hash + description
* Date and time
* Clear distinction between stable and development versions
* Easy switch functionality for each commit

Source: #temp-desktop-bug-dump thread, June 3 2026.

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*Migrated from Linear: [DESK2-114](https://linear.app/comfyorg/issue/DESK2-114/implement-full-version-control-ui-for-comfyui-core-commit-timeline)*