fix(core): support numeric strings in min and max validation

[ken8203]

Summary

• Allow the built-in min and max validators to evaluate finite numeric strings.
• Continue rejecting empty strings, whitespace, non-numeric strings, booleans, NaN, and Infinity.
• Document the updated range validation behavior.

Motivation

HTML inputs store their values as strings, including <input type="number">. The shadcn renderer therefore writes values such as "12" to state.

The built-in min and max validators currently accept only JavaScript numbers, so a valid number input can fail both range checks:

builtInValidationFunctions.min("12", { min: 0 }); // false
builtInValidationFunctions.max("12", { max: 120 }); // false

This change safely converts non-empty numeric strings before comparison while avoiding broad JavaScript coercion for values such as "", false, or null.

Related but non-overlapping: #306 tightens the standalone numeric validator. This PR only addresses range validation for input values.

Testing

• vitest run packages/core/src/validation.test.ts --environment node --maxWorkers 1 — 103 tests passed
• pnpm --filter @json-render/core build
• Prettier check for the changed TypeScript files

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