feat: UTM builder tool and naming standard

[thalescb]

Adds a self-contained UTM URL builder and org-wide naming standard for campaign attribution.

What's included

• UTM Builder (tools/utm-builder/index.html) — dark-mode web tool with dropdown validation, tooltips, and copy-to-clipboard. Enforces the naming convention so nobody can free-type broken UTMs.
• Config (tools/utm-builder/config.json) — controlled values for sources, mediums, initiatives, and goals. Edit this file to add/remove options; the builder reads it at runtime.
• UTM Master Standard (tools/utm-builder/UTM_STANDARD.md) — the reference doc explaining rules, governance, and per-channel conventions.

How it works

1. Open the builder page
2. Fill dropdowns + campaign name
3. Copy the generated URL
4. Share it

Config.json is the single source of truth for valid values. The builder renders them as dropdowns and in a collapsible reference section.

Deployment

Designed for GitHub Pages at /utm-builder/. Workflow update to add it alongside dbt docs coming in a follow-up.