Improvement: protect plan files from review deletion (#142)

* fix: protect plan and solution files from review/resolve deletion

The review/resolve pipeline could flag docs/plans/*.md and
docs/solutions/*.md files for deletion, contradicting /workflows:work
which treats them as living documents.

Adds protection at three layers:
- review.md: Protected Artifacts section + synthesis filter
- code-simplicity-reviewer.md: YAGNI exception for pipeline artifacts
- resolve_todo_parallel.md: Safety check to skip/wont_fix such todos

Fixes #140

* fix: protect plan and solution files from review/resolve deletion

The review/resolve pipeline could flag docs/plans/*.md and
docs/solutions/*.md files for deletion, contradicting /workflows:work
which treats them as living documents.

Adds protection at four layers:
- review.md: Protected Artifacts section and synthesis filter
- code-simplicity-reviewer.md: YAGNI exception for pipeline artifacts
- resolve_todo_parallel.md: Skip and wont_fix todos targeting these paths
- git-history-analyzer.md: Note not to characterize them as unnecessary

Fixes #140

---------

Co-authored-by: Axl Ottle <axl@Axls-Virtual-Machine.local>

plugins/compound-engineering/agents/review/code-simplicity-reviewer.md

@@ -33,6 +33,7 @@ When reviewing code, you will:
    - Eliminate extensibility points without clear use cases
    - Question generic solutions for specific problems
    - Remove "just in case" code
+   - Never flag `docs/plans/*.md` or `docs/solutions/*.md` for removal — these are compound-engineering pipeline artifacts created by `/workflows:plan` and used as living documents by `/workflows:work`
 
 6. **Optimize for Readability**:
    - Prefer self-documenting code over comments