Fix pool performance metrics for bounded periods

[18166714330cl-maker]

Fixes #6

This adjusts pool performance calculations so weekly/monthly/yearly metrics use only the selected stat window and numeric arithmetic.

Changes:

• avoid mutating the shared oldest index while iterating assets
• sum deposits/withdrawals only across the selected performance window
• coerce stat values to numbers before arithmetic to avoid string concatenation in reducers

Validation:

• npm run build

[18166714330cl-maker]

Quick follow-up: I rechecked the failing status. The Vercel check is failing with "Account is blocked", which appears to be an external Vercel account/deployment issue rather than a failure caused by this code change. I also verified locally that npm run build passes for this PR.