codemap --diff output unbounded in showDiffVsMain

[JordanCoin]

Problem

In cmd/hooks.go:231, for repos under 5000 files, showDiffVsMain runs codemap --diff and pipes directly to stdout without the 60KB hard cap.

The tree output path captures into a buffer and truncates, but the diff path does not. On a branch with many changed files in a medium-sized repo, this could produce unexpectedly large output.

Suggested fix

Capture codemap --diff output into a buffer and apply the same limits.MaxContextOutputBytes truncation used for tree output.

Context

Flagged during review of #22. Low risk since it only applies to repos under 5000 files, but inconsistent with the tree output which has the hard cap.