[Feature] Add size converter

[yeleepark]

Summary

Add a Size Converter for translating common clothing and shoe sizes across regional sizing systems.

Why

Size conversion is useful for online shopping, travel, gifts, resale listings, and international product comparisons. It is a broadly accessible everyday utility that fits oddkit's lightweight browser-tool direction.

Proposed scope

• Convert shoe sizes across KR, US, EU, UK, and JP systems
• Convert clothing sizes across common regional labels where feasible
• Support gender/category selection when size systems differ
• Show clear caveats that brand sizing can vary
• Copy converted size results to the clipboard
• Process everything locally in the browser

UX notes

• Keep category, region, and size controls compact
• Make sizing caveats visible but not intrusive
• Consider separate tabs for shoes and clothing
• Suggested microcopy: // sizes, translated

Acceptance criteria

• Users can enter a size and convert it across supported regions
• Shoe and clothing conversions are clearly separated where needed
• Unsupported or ambiguous inputs show useful guidance
• Results can be copied to the clipboard
• No input data is uploaded to a server