fix: validate OINK with cold module caches

[imbajin]

Problem and fix

Before	After
Cold Hugo module initialization writes progress to stdout, causing the graph gate to reject a valid dependency graph after merge	Use native --quiet while retaining strict dependency and version checks
A passing PR relied on restored cache contents without exercising module initialization	Both PR and push jobs verify the existing cache and an independent empty Hugo cache

Add a real Hugo empty-module-cache regression that checks the graph and preserves the original lock files. Focused upgrade tests and link validation pass. Site content and the theme version are unchanged.