refactor(opencode): parallelize git snapshot operations on finish-step

[robertkohahimn]

Issue for this PR

Closes #12437

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

On every LLM finish-step, the processor called Snapshot.track() then Snapshot.patch() sequentially. Both called git add . internally, so the worktree was staged twice with no files changing in between.

This PR adds trackAndPatch() which calls git add . once, then runs git write-tree and git diff --name-only concurrently via Promise.all. The standalone track() and patch() functions are unchanged for other callers.

How did you verify your code works?

• Read both call sites in processor.ts to confirm trackAndPatch produces the same hash and patch data as the previous sequential calls
• Verified patch() and track() remain unchanged for other callers (revert, debug CLI)
• Confirmed no type errors in the changed files

Screenshots / recordings

N/A — no UI changes.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[github-actions]

Hey! Your PR title perf(opencode): parallelize git snapshot operations on finish-step doesn't follow conventional commit format.

Please update it to start with one of:

• feat: or feat(scope): new feature
• fix: or fix(scope): bug fix
• docs: or docs(scope): documentation changes
• chore: or chore(scope): maintenance tasks
• refactor: or refactor(scope): code refactoring
• test: or test(scope): adding or updating tests

Where scope is the package name (e.g., app, desktop, opencode).

See CONTRIBUTING.md for details.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍