Sync third-party and MCP marketplace plugins

Constraint: Public skills are published only by explicit administrator action unless they are tracked third-party market sources.
Confidence: high
Scope-risk: narrow
Directive: Keep private/internal skills out of the public marketplace and preserve normal incremental market Git history.
Tested: Marketplace validation passed.

config/skill-overrides/xlsx/recalc.py

@@ -30,6 +30,8 @@ def inspect_workbook(path):
                     cached = values[sheet.title][cell.coordinate]
                     if cached.data_type == "e":
                         errors.setdefault(str(cached.value), []).append(location)
+                    elif cell.data_type == "f" and cached.value is None:
+                        errors.setdefault("MISSING_FORMULA_CACHE", []).append(location)
         return formula_cells, errors
     finally:
         formulas.close()