feat: fhirlint.yml composer — visual config builder

[predictor2718]

Goal

A form-based wizard that lets users build a fhirlint.yml without knowing the schema by heart. Fills the gap for teams onboarding to fhirlint who aren't familiar with all available options.

UI

Left side: form with all supported config fields

• FHIR version (dropdown: 4.0.1, 4.3.0, 5.0.0)
• Severity (dropdown)
• Fail-on (dropdown)
• Profiles (multi-select with built-in aliases: kbv-basis, mii, diga + free-text for custom URLs)
• IGs (repeatable text input)
• Terminology server toggle + custom URL
• Best-practice handling (dropdown)
• Suppress rules (repeatable: type + value)
• Timeout, locale, tx-cache, allow-example-urls, cache

Right side: live YAML preview — updates as the user fills in the form

Bottom: "Copy YAML" and "Open in Validator →" buttons

Notes

• Purely client-side — no backend needed
• "Open in Validator →" should pre-fill the options panel on the validate page and optionally pass the config as a parameter (see related issue)
• Related to #59 in the main repo (fhirlint init CLI command)