feat(mint): add @property type-check analysis to CSS audit

[nujovich]

Card: https://github.com/nujovich/mint-radar/issues/8\n\n**What:** Extends the CSS audit with @Property type-check analysis. Milestone 1\nadds a new audit step to that detects CSS @Property\nregistrations, validates usage against declared syntax, and flags\ntype mismatches. The feature leverages Mint's existing LLM-based audit\npipeline (Claude) — no new runtime parser needed.\n\nWhy: @Property adoption is growing (2.67% per Project Wallace 2026, driven\nby Tailwind v4). Mint currently audits colors, fonts, spacing, line-height,\nmotion, layout accessibility, modern practices, and overflow safety, but has\nno awareness of registered custom properties or their type contracts. Adding\n@property validation catches a class of bugs (type mismatches between\ndeclared syntax and actual var() usage) that neither ESLint CSS nor Stylelint\ntarget natively, reinforcing Mint's differentiation as a semantic auditor.\n\n## Milestones\n\n- [x] Milestone 1 — Extend audit prompt in lib/prompts.mjs with @Property\n analysis step: detect @Property registrations, validate var() assignments\n against declared syntax, report type mismatches\n\n- [x] Milestone 2 — Add @Property type-check fields to AuditReport type in\n lib/types.ts\n\n- [x] Milestone 3 — Wire @Property results in the playground UI (app/page.tsx)\n\n- [x] Milestone 4 — Add test fixture with @Property examples in\n lib/fixtures/ and corresponding test in lib/tests/\n\nHow to test:\n

[nujovich]

All milestones complete. Ready for review when you are.

[nujovich]

All milestones complete. Ready for review when you are.

[nujovich]

All milestones complete. Ready for review when you are.