chore(demo): add multi-feed, cash-out, and dispute demo scenarios

[Neziahtech]

closes #426

Summary

Extends scripts/demo_scenarios/ with three new scenarios covering multi-feed
settlement, cash-out, and dispute flows, for hackathon/demo purposes.

New Scenarios

1. Multi-feed

• Script: scripts/demo_scenarios/<name>.ts|sh
• What it demonstrates: <e.g. settlement across multiple price feeds, feed disagreement handling>
• Expected output: <deterministic expected values/log>

2. Cash-out

• Script: scripts/demo_scenarios/<name>.ts|sh
• What it demonstrates: <e.g. early exit/cash-out pricing and settlement>
• Expected output: <deterministic expected values/log>

3. Dispute

• Script: scripts/demo_scenarios/<name>.ts|sh
• What it demonstrates: <e.g. commit-reveal dispute raised, resolved, funds released correctly>
• Expected output: <deterministic expected values/log>

Determinism

• All scenarios use fixed seeds/inputs so output is reproducible across runs
• <how randomness, if any, is seeded>

README

• Updated scripts/demo_scenarios/README.md with:
  • How to run each new scenario (<command>)
  • Expected output for each, so a run can be diffed against expected results
  • Any prerequisites (local node, funded test accounts, etc.)

Test Evidence

```
<command to run each new scenario + captured output matching documented expected output>
```

Commands Run

```
<formatter + result>
<lint + result>
<build + result>
<existing test suite (to confirm no regression) + result>
```

Scope Confirmation

• No unrelated refactors
• No formatting-only changes bundled in
• No generated artifacts or secrets included
• No disabled checks
• Scenarios are demo/ops scripts only — no production contract logic changed