[Feature] Add UTM builder

[yeleepark]

Summary

Add a UTM builder for creating campaign tracking URLs from a base URL and common UTM parameters.

Why

UTM links are frequently used by marketing, operations, content, and product teams to track where traffic comes from across newsletters, social posts, ads, partner links, QR codes, and launch campaigns. A small local builder helps avoid manual URL mistakes and makes campaign links faster to create.

Proposed scope

• Accept a base URL
• Support common UTM fields: source, medium, campaign, content, and term
• Preserve existing query parameters on the base URL
• Encode parameter values safely
• Generate a final campaign URL
• Copy the generated URL to the clipboard
• Show clear validation errors for invalid URLs
• Process everything locally in the browser

UX notes

• Keep the base URL and generated URL visible at the same time
• Use compact form controls for UTM fields
• Consider lightweight presets for common mediums such as email, social, paid, referral, and QR
• Suggested microcopy: // campaign links, less guesswork

Acceptance criteria

• A valid base URL and UTM fields produce a correctly encoded URL
• Existing query parameters are preserved when UTM parameters are added
• Empty optional UTM fields are omitted from the final URL
• Invalid URLs show a useful error state without crashing
• The generated URL can be copied to the clipboard
• No input data is uploaded to a server