feat: integrate push into update_job_status DONE transition

On status=done, calls pushBranchForJob before DB write:
- pushed=true → DONE + pushed_at + branch set + worktree cleanup (keepBranch=true)
- no-changes → DONE without pushed_at + worktree cleanup
- push failure → FAILED with error message + worktree preserved for manual inspection

Also adds pushed_at to vendored prisma schema + regenerates client.
6 unit tests for prepareDoneUpdate covering all push outcomes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/schema.prisma

@@ -256,6 +256,7 @@ model ClaudeJob {
   claimed_at          DateTime?
   started_at          DateTime?
   finished_at         DateTime?
+  pushed_at           DateTime?
   plan_snapshot       String?
   branch              String?
   summary             String?