[Feature] Add recipe scaler

[yeleepark]

Summary

Add a Recipe Scaler for adjusting ingredient amounts when changing the number of servings in a recipe.

Why

Recipe scaling is useful for everyday cooking, meal prep, small gatherings, and content creators sharing recipes. It is a broadly accessible utility that fits oddkit's lightweight browser-tool direction beyond developer-focused workflows.

Proposed scope

• Enter the original serving count and target serving count
• Add ingredient rows with amount, unit, and ingredient name
• Recalculate ingredient quantities based on the serving ratio
• Support common fractional quantities where practical
• Copy the scaled recipe to the clipboard
• Process everything locally in the browser

UX notes

• Keep the original and scaled amounts easy to compare
• Use compact rows for ingredient entry
• Consider quick controls for doubling, halving, and common serving counts
• Suggested microcopy: // dinner math, handled

Acceptance criteria

• Ingredients scale correctly when changing serving counts
• Decimal and common fractional amounts are handled gracefully
• Empty or invalid rows do not crash the tool
• Scaled output can be copied to the clipboard
• No recipe data is uploaded to a server