Autofix: Race condition with autofix:clean label on bootstrap PRs

[stranske]

Summary

When a PR is created with just a bootstrap commit (minimal or no code), autofix runs and finds "no changes required". It then adds the `autofix:clean` label per line 878-880:

if (!changed) {
  desired.add(cleanLabel);  // cleanLabel = 'autofix:clean'
}

When the real code is pushed (with formatting issues), autofix re-runs but now sees the `autofix:clean` label and enters clean mode which only does a cosmetic sweep.

Root Cause

Timeline example from Manager-Database PR #55:

1. 21:52:57 - Bootstrap commit created (empty/minimal code)
2. 21:54:03 - First autofix runs, finds "no changes" → adds `autofix:clean` label
3. 22:02:12 - Real code pushed with black formatting issues
4. 22:02:34 - Second autofix runs, but now in clean mode (due to label) → finds "Clean-mode cosmetic sweep found no changes"
5. Gate fails because black formatting issues were never fixed

Impact

• PRs created by Codex agent often have this problem since they start with bootstrap commits
• Users have to manually remove the `autofix:clean` label to trigger a full autofix

Proposed Fix

Option A: Do not add `autofix:clean` label when autofix finds no changes
Option B: Remove `autofix:clean` label when new commits are pushed
Option C: Detect bootstrap commits and skip label management

Related

Also related: Autofix only targets hardcoded paths (src, tests, tools, streamlit_app, .github/scripts) - projects with different structures like `api/`, `adapters/`, `etl/` are not checked.