Template:TissueDB Simulator Layout/sandbox

This is the sandbox version for testing v3.6 hardening changes.

Changes from v3.5:

• Required parameter validation: procedure, difficulty, build_time, cost — missing params trigger maintenance category + inline warning
• Hero image empty state fix: suppress broken [[File:]] link when hero_image is empty
• Documentation comments added for editor guidance
• No breaking changes to existing pages with complete parameters