Add construction-schedule-review skill

Skill for reviewing Primavera P6 XER construction schedules:
- Critical path analysis
- Milestone status review
- Relationship analysis (lead/lag, out-of-sequence)
- In-progress duration checks
- CPM narrative validation

Uses xer-mcp server for schedule data queries.

.gitmodules

@@ -19,3 +19,6 @@
 [submodule "grist-accounting"]
 	path = grist-accounting
 	url = https://git.prettyhefty.com/Bill/grist-accounting.git
+[submodule "construction-schedule-review"]
+	path = construction-schedule-review
+	url = https://git.prettyhefty.com/Bill/construction-schedule-review.git