Fix Git Graph UI showing HEAD instead of selected commit

[exedev-shelley]

Author: weijunw
Channel: #feedback
Link: https://discord.com/channels/1405685085923049482/1405686161791516873/1527733988356002013

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Description

Bug in Shelley's Git Graph UI when selecting commits outside the most recent 20 commits window.

Steps to Reproduce

1. Open Git Graph
2. Select a commit among the most recent 20 commits
3. Click Open Diff → The commit is shown correctly
4. Select an older commit (beyond that recent 20 window)
5. Click Open Diff → It shows HEAD instead of the selected commit

Expected Behavior

Opening diff for an older commit should display that specific commit, not HEAD.

Actual Behavior

When selecting a commit outside the most recent 20 commits and clicking Open Diff, the UI displays HEAD instead of the selected commit.