Add projectRates snapshot tests

[Sikkra]

Resolves #75.

Summary:

• Added a Vitest snapshot suite for projectRates with 12 deterministic cases.
• Covered both sides of the 50% target-utilization kink and the 95% steep-slope kink.
• Added test:project-rates and one-line test:project-rates:update scripts.
• Fixed existing frontend type-check blockers so the snapshot branch passes tsc: .ts source imports, wallet auth modal params, and demo ReserveStats mocks.

Verification:

• npm run test:project-rates
• npx tsc --noEmit
• npm run build
• git diff --check