git_ui: Fix history tab empty and detached HEAD states

[Revantark]

This PR fixes a few History tab edge cases in the Git Panel.

For a fresh repo with no commits, the History tab now finishes loading and shows No commits yet instead
of sitting on Loading… indefinitely or falling into a misleading empty/error state.

It also fixes detached HEAD history loading. In that case, the Git Panel asks the backend to load history
from the current commit SHA. The local git backend was accidentally treating the raw object ID bytes as a
string instead of formatting them as a normal hex SHA, so git log could fail before returning any
commits. The backend now passes the SHA in the format git expects.

Repro for empty repo:

mkdir /tmp/zed-empty-history
cd /tmp/zed-empty-history
git init
zed .

Open Git Panel → History.

Before: History could stay stuck on Loading….
After: History shows No commits yet.

Repro for detached HEAD:

mkdir /tmp/zed-detached-history
cd /tmp/zed-detached-history
git init
echo hi > file
git add file
git commit -m initial
git checkout --detach HEAD
zed .

Open Git Panel → History.

Before: History could fail to load commits.
After: History shows the commit history normally.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Release Notes:

• Fixed Git history tab states for empty repositories and detached HEAD history.

[smitbarmase]

Thanks. I fixed a few conflicts after the rebase and added supporting tests.

[Revantark]

@smitbarmase thanks and I can take a look at tests tomorrow and patch them up.

[Revantark]

@smitbarmase updated

[dinocosta]

@smitbarmase Let me know if you eventually want to take a look at this one together. I was also considering reviewing #60537 before Kunall pointed me to this one 🙂

[smitbarmase]

I think CI was failing on a test I couldn’t spend time figuring out. I can take a look today, or lets pair on it.