feat(projman): add sprint lifecycle state machine via milestone metadata

- New skill: sprint-lifecycle.md defines states, transitions, and check protocol
- All sprint commands now check and set lifecycle state
- States tracked in milestone description metadata (Sprint/Planning, Sprint/Executing, Sprint/Reviewing)
- Out-of-order calls produce warnings with guidance
- --force override available for all lifecycle checks
- Added Sprint/* labels to label taxonomy documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/projman/commands/review.md

@@ -8,6 +8,7 @@ agent: code-reviewer
 ## Skills Required
 
 - skills/review-checklist.md
+- skills/sprint-lifecycle.md
 
 ## Purpose
 
@@ -19,6 +20,7 @@ Run `/review` before `/sprint-close` to catch issues.
 
 ## Workflow
 
+0. **Check Lifecycle State** - Execute `skills/sprint-lifecycle.md` check protocol. Expect `Sprint/Executing`. Set `Sprint/Reviewing` after review begins. Warn if in wrong state (allow with `--force`).
 1. **Determine Scope** - Sprint files or recent commits (`git diff --name-only HEAD~5`)
 2. **Read Files** - Use Read tool for each file in scope
 3. **Scan for Patterns** - Check each category from review checklist