* Limit large git diff payloads in main process before IPC transfer
Move the large diff rendering limit check to a shared module so that
the main process can evaluate diff sizes before transferring them. If
a diff exceeds the limits, its text content is dropped prior to IPC
serialization, and only the limit metadata is sent. This prevents the
application from freezing or crashing when loading massive diff files.
* Gracefully handle and prune oversized files in diff viewer
Prevent UI freezes and out-of-memory errors when viewing or editing
extremely large diffs or files. Working-tree files above 10MB and git
buffer overflows are treated as binary. Text diffs exceeding safe
rendering limits have their contents pruned before IPC transport, and
the UI is updated to show fallback states and disable invalid saves.
* Document save action check for large diffs and fix test import
Explain why saveContentAvailable is required for oversized diffs, as
stripped text bodies before IPC prevent complete saves. Also update the
large-diff-render-limit import in E2E tests to use the shared path.
Jinjing