fix(merch): reject non-decimal numeric options

[aiirvizionz]

Summary

• add strict parsers for merch quantity, price, markup, and budget cap options
• reject scientific and hexadecimal numeric strings that JavaScript Number() would otherwise accept
• add direct regression coverage for merch numeric options

Tests

• node_modules/.bin/vitest.CMD run packages/cli/src/commands/merch.test.ts
• node_modules/.bin/tsc.CMD -p packages/cli/tsconfig.json --noEmit
• git diff --check