Fix reverse sync missing human commits when mono-filtered advances

--ancestry-path returns empty when mono-filtered/main has advanced
past the last forward sync (any monorepo commit causes josh to create
a new filtered SHA not in the subrepo's ancestry). Use git merge-base
to find the last connected point instead.

Also return skip-dirty (not skip) when trees differ but no human
commits found, preventing state from being updated on false skips
which would permanently lose unsynced commits.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -6,10 +6,16 @@
 
 - **Linearize fallback for reverse sync**: When josh-proxy rejects a push due to unmappable merge commits, reverse sync automatically falls back to linearizing the history — cherry-picking regular commits individually and squashing only the problematic merge commits via `cherry-pick -m 1`. Preserves individual commit granularity while handling complex merge topologies that josh cannot map. PR body notes when linearization was used.
 
+### Fixes
+
+- **Reverse sync human commit detection**: Fixed `--ancestry-path` returning empty when `mono-filtered` has advanced past the last forward sync. Any monorepo commit (even outside the subfolder) causes josh to create a new filtered commit, breaking the ancestry path to subrepo HEAD. Now uses `git merge-base` to find the last connected point.
+- **State not updated on false skip**: When trees differ but no human commits are found, reverse sync now returns `skip-dirty` instead of `skip`. State is not updated, so the system retries on the next run instead of silently dropping commits.
+
 ### Docs
 
 - Expanded troubleshooting guide for "Josh rejected push" with root cause analysis and prevention advice.
 - Added ADR-011: Linearize fallback for reverse sync.
+- Added recommended Git workflow section to the guide.
 
 ## 1.2.0