Function getDemoBlockRaised

Deterministic "amount raised in this schedule block" for demo mode.

Backs useCurrentBlockRaised when it's driven in demo mode so QA can visually verify that the raised-amount label transitions in lockstep with the current block. The value is derived purely from the block's starts_at timestamp so:

• Each block in a buildDemoSchedule output produces a distinct number (consecutive slots have distinct starts_at).
• The same block always resolves to the same amount — no jitter between renders inside a slot, which would otherwise mask genuine transition bugs.

Amounts land in the $100–$5 000 range so the demo campaign's $5 000 goal bar visibly moves as blocks roll over.

Pure function — no fetching, no clock reads.