feat(orchestrator): add single-cycle PR revision on CHANGES_REQUESTED review

[Maxtanh-Meta]

Summary

When a human submits a CHANGES_REQUESTED review on a symphony-go PR, the orchestrator now detects it via polling and runs a single revision cycle on the existing branch — updating the PR in place instead of closing and reopening.

How it works

1. PollPRRevisions (new tick step after PollApprovals) scans pr_ready jobs for fresh CHANGES_REQUESTED reviews submitted after job.UpdatedAt
2. runPRRevision drives the implementation agent with a revision prompt containing the original issue, approved plan, and reviewer feedback
3. The agent's changes are committed and pushed to the same branch (no new PR)
4. Job.RevisionAttempted = true — only one revision cycle runs per PR; subsequent reviews are left for human follow-up

Design decisions

• Single cycle only: Avoids infinite revision loops. After one revision attempt, the job stays terminal (pr_ready)
• Reuses existing infrastructure: Same worktree, same branch, same implementation agent runner
• Non-destructive: Labels unchanged, PR stays open, no close/reopen
• Staleness guard: Reviews submitted before job.UpdatedAt are ignored (prevents acting on old feedback)
• Self-bot filter: Reviews from ignored users (bot accounts) are skipped via isIgnoredApprovalUser

Changes

• internal/github/github.go — Add PRReview type + ListPRReviews to Client interface
• internal/github/fake.go — Add SeedPRReview + ListPRReviews to InMemoryFake
• internal/types/types.go — Add RevisionAttempted field to Job
• internal/orchestrator/loop.go — Call PollPRRevisions in tick
• internal/orchestrator/revision.go (new) — Polling + execution logic
• internal/orchestrator/revision_test.go (new) — 3 test cases

Tests

All 3 new tests pass:

• TestPollPRRevisions_HappyPath — full revision cycle commits + pushes
• TestPollPRRevisions_RevisionAttemptedSkips — second revision blocked
• TestPollPRRevisions_StaleReviewIgnored — old reviews ignored