docs(sw): define header tool icon reuse and window control rules
- AI_USAGE §5: single rule for design-based header tools (icon priority
1-3, Storybook fixtures vs public API, pill icon states, window control
omission via hiddenControls, existing-screen preservation, web/desktop)
- Reference §5 from AI_GUIDE (+4 synced copies), COMPOSITION_PATTERNS,
COMPONENT_CATALOG, DESIGN_RULES §9
- Process header spec §13: Figma tool icon export on hold, proposed
swProcessToolIcons and preconditions (no source/API change)
shkim4
9a861a8d55