fix: reject blank numeric CLI values

[Ghraven]

What changed

• Reject empty or whitespace-only values in the shared numeric CLI validator.
• Added a regression test for blank numeric values.
• Rebuilt dist/cli.js so the published CLI bundle matches the source change.

Problem

validateNumberInput() used Number(value) directly. In JavaScript, Number("") and Number(" ") both evaluate to 0, so blank input could be accepted as a valid numeric value for options using this shared validator, such as --min-width and --min-height.

Before / after

Before:

• validateNumberInput("") returned 0.
• validateNumberInput(" ") returned 0.

After:

• Blank or whitespace-only numeric values throw InvalidArgumentError("Not a number.").
• Existing valid values like 1200 and 0 keep working.

Verification

• corepack pnpm exec vitest run tests/unit/cli-options.test.ts → 9 tests passed.
• corepack pnpm run cli:build completed successfully and regenerated dist/cli.js.
• git diff --check passes.