send full diff to PR title/body generator

[adboio]

Problem

pr title/body LLM call only sends a "summary" with commit messages and changed file paths, so it often hallucinates changes

the diff check is also not accurate to what will actually be in a PR against the default

Changes

updates diff checking, sends actual diff content to llm

How did you test this?

manually

[adboio]

• feat(code): disable editing in diff viewer #1395 : 2 dependent PRs (#1397 , #1409 )
• feat(code): unified PR creation workflow #1377
• send full diff to PR title/body generator #1394 👈 (View in Graphite)
• fix(code): dedupe suggested branch names #1393
• fix(code): increase diff scan limit #1392
• main

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[adboio]

Merge activity

• Mar 31, 8:47 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Mar 31, 8:56 PM UTC: Graphite couldn't merge this pull request because a downstack PR fix(code): dedupe suggested branch names #1393 failed to merge.
• Apr 1, 7:08 AM UTC: @adboio merged this pull request with Graphite.

The base branch was changed.