feat(studio): record staged edit outcomes

[w1ne]

Summary

• add bounded in-memory applied edit history to the Studio shell store
• record approve/reject/rerun outcomes with prompt, source, target, generation, and changed-line evidence
• render recent edit outcomes under the staged edit controls and update approved entries from validator results

Test Plan

• npm test -- --run src/studio/tests/shellStore.test.ts src/studio/tests/StagedEditSlot.test.tsx
• npm run typecheck
• git diff --check
• npm run build:studio
• npm run lint (passes with existing unused-disable warnings outside this slice)

Private docs: w1ne/kernelCAD-private@792663b