feat(mint): add logical properties migration audit types and mapping

[nujovich]

Card: https://github.com/nujovich/mint-radar/issues/19

What: Adds a deterministic logical properties migration audit to Mint. Milestone 1 introduces the LogicalPropertyIssue, LogicalPropertyAudit, and PHYSICAL_TO_LOGICAL mapping types in lib/types.ts, plus the logicalProperties field on AuditReport. The mapping covers 30+ physical CSS properties and their flow-relative equivalents (e.g. margin-left -> margin-inline-start, padding-right -> padding-inline-end, left -> inset-inline-start), plus directional keyword mappings (text-align: left -> text-align: start). Future milestones will implement the parser, wire CLI output, and add Stylelint 17.10-aligned tests.

Why: Stylelint 17.10 standardized logical property enforcement with three new rules (property-layout-mappings, unit-layout-mappings, value-keyword-layout-mappings). Mint's CSS audit needs a deterministic analyzer that detects physical directional properties and guides users toward flow-relative equivalents for automatic RTL/LTR and writing-mode support. The deterministic approach complements the existing LLM-based STEP 14 analysis (from card #10) by providing instant, syntax-level detection without LLM latency or cost.

Milestones

• Milestone 1 -- Add LogicalPropertyIssue, LogicalPropertyAudit, and PHYSICAL_TO_LOGICAL mapping to lib/types.ts; add logicalProperties field to AuditReport
• Milestone 2 -- Implement lintLogicalProperties() in lib/css-lint-rules.mjs: parse CSS, detect physical properties where flow-relative equivalents exist, emit issues with selectors and suggestions
• Milestone 3 -- Wire logicalProperties into bin/mint-ds.mjs CLI output and audit-summary.mjs as a lint category with migration ratio display
• Milestone 4 -- Add test fixture with mixed logical/physical CSS and tests referencing Stylelint 17.10 logical-properties rules

How to test:

npx vitest run lib/__tests__/css-lint-rules.test.mjs
# After milestone 3:
node bin/mint-ds.mjs lint <directory-with-physical-css>

[nujovich]

All milestones complete. Ready for review when you are.