fix(cli): validate positive numeric options

[lazyGPT07]

Summary

• reject empty, malformed, fractional, zero, negative, and non-finite CLI numeric options
• apply one shared positive-integer parser to board reads and feed limits/freshness
• add focused parser regression tests

Validation

• vitest run packages/cli/src/numeric-options.test.ts packages/cli/src/index.test.ts (12 tests passed)
• tsc -p packages/cli/tsconfig.json --noEmit

Closes #48