Replace hard-coded Scenario block fixture

[ApocDev]

Two existing mutating Scenario E2E cases depend on block id 83 being a Coal gas fixture copied from the active project:

• Scenario scales a goal beyond recovered coproduct supply
• Scenario explains which proposed block goals failed validation

The current seed no longer contains that block, so both tests fail before opening the page. Make these cases seed their own deterministic blocks and flows (as the adjacent unpinned-consume test does) instead of depending on a user-project row id.

Discovered while validating #156; the new cache/progress Scenario flows pass independently.