fix(cli): allow zero layout tolerance

[tianma-if]

Summary

• preserve an explicit --tolerance 0 for layout inspection
• continue clamping negative values to zero
• retain the default tolerance of 2 for invalid input

Why

The previous parseFloat(value) || 2 expression treated a valid zero as missing, so callers could not request exact, zero-tolerance overflow checks.

Validation

• bunx oxfmt packages/cli/src/commands/layout.ts packages/cli/src/commands/layout.test.ts
• bunx oxlint packages/cli/src/commands/layout.ts packages/cli/src/commands/layout.test.ts
• bun run --filter @hyperframes/cli test -- layout.test.ts
• bun run --filter @hyperframes/cli typecheck