chore(qa): move Ethos design kit out of frontend/ into tracked design-system/

The kit (SKILL.md, ethos.tokens.css, ethos-icons.svg, .oxlintrc.json) lived
inside frontend/ — the exact dir freestyle runs scaffold into. vite refuses a
non-empty target, so every session improvised a stash-aside (frontend_backup/,
frontend_temp/) and left scratch dirs behind. Move the kit to a sibling
design-system/ so frontend/ starts clean, and deliver it via the L0 conventions
channel (project.toml) rather than seeding files in the scaffold target: copy
the token/icon assets in (don't read them), SKILL.md for rules only. Un-ignore
frontend/ so scaffolded output is tracked going forward.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HMbPmZZjcXhR2crU82zZ8S

.correx/project.toml

@@ -6,6 +6,7 @@ conventions = [
     "No bare try-catch; use runCatching and sealed domain error types",
     "Every new EventPayload must be registered in the eventModule polymorphic block (Serialization.kt)",
     "Track multi-session or handoff work as native tasks: search before creating to avoid duplicates (task_search), task_context before starting, claim before working, submit_for_review when ready, complete after review. Don't open a task for a single self-contained edit you finish now. When a goal has dependency seams or independent review points, task_decompose it into a parent + DEPENDS_ON-linked children (one approval) instead of one big task; a session works one task at a time, so siblings are claimed by later runs as they unblock.",
+    "UI uses the Ethos design system in ./design-system. COPY design-system/ethos.tokens.css and ethos-icons.svg into the project and import them — do NOT read their contents. All colors/spacing/radii come from the token CSS vars (never hardcode). Read design-system/SKILL.md only for component/layout rules.",
 ]
 
 [commands]