feat(code): add git diff head query

[adboio]

Problem

in #1410 i am adding a new diff viewer

it needs to be very fast

we don't have a sufficiently-fast query yet

Changes

adds a new query getDiffHead to slurp up the whole diff in one query

How did you test this?

[adboio]

• feat(code): add comment-to-agent in diff viewer #1416
• fix(code): fix timestamp hover #1415
• feat(code): replace in-chat diffs with pierre/diffs #1414
• feat(code): replace diff editor with unified review panel #1410
• feat(code): add git diff head query #1412 👈 (View in Graphite)
• get full list of changed files #1411
• chore: extract some utils #1409
• feat(code): disable editing in diff viewer #1395 : 1 other dependent PR (#1397 )
• feat(code): unified PR creation workflow #1377
• send full diff to PR title/body generator #1394
• fix(code): dedupe suggested branch names #1393
• fix(code): increase diff scan limit #1392
• main

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[jonathanlab]

Merge activity

• Apr 1, 10:51 AM UTC: A user started a stack merge that includes this pull request via Graphite.
• Apr 1, 11:15 AM UTC: Graphite rebased this pull request as part of a merge.
• Apr 1, 11:20 AM UTC: @jonathanlab merged this pull request with Graphite.