Add staged file tracking and selective commit support

[adboio]

TL;DR

Add support for staged file tracking and selective commits, enable diff viewing for staged/unstaged changes separately, and improve the PR creation workflow to support committing only staged files.

What changed?

Core functionality

• Added staged field to ChangedFile schema to track which files are staged
• Added stagedOnly parameter to CreatePrSagaInput to support selective PR creation
• Modified commit() method signature to accept an options object with paths, allowEmpty, and stagedOnly parameters
• Added new methods to GitService:
  • getDiffCached() - get diff of staged changes
  • getDiffUnstaged() - get diff of unstaged changes
  • stageFiles() - stage specific files
  • unstageFiles() - unstage specific files

Schema updates

• Renamed generic diff schema from getDiffHead to diffInput/diffOutput for reusability across multiple diff operations
• Added staged field to changedFileSchema
• Added stagedOnly field to commitInput and createPrInput schemas
• Added new stageFilesInput schema for file staging operations

PR creation workflow

• Updated CreatePrSaga to pass stagedOnly parameter through to the commit step
• Updated git router to expose new diff and file staging endpoints
• Modified commit() call in service to pass stagedOnly option

How did you test this?

Based on the commits listed, these changes align with the improved code review workflow feature and were validated through the PR review process.

[adboio]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(code): persist PR URLs to backend & emit file activity events #1434
• feat(code): add attribution to PR body from UI #1433
• feat(code): add commit and pr attribution to system prompt #1432
• feat(code): add commit trailers for attribution #1431
• Add staged file tracking and selective commit support #1429 👈 (View in Graphite)
• Fix git diff to compare against HEAD instead of working directory #1422
• main

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