feat: add @script-development/fs-toast package

[Goosterhof]

Summary

• New @script-development/fs-toast package — component-agnostic toast queue service for Vue 3
• Generic factory (createToastService<C>) manages a FIFO queue; consumer provides their own toast component and mounts the container
• Zero fs-* dependencies — only peer dep is Vue 3.5+
• 15 tests, 100% coverage, 90% mutation score

Design decisions

• "Mount it yourself" — returns a ToastContainerComponent the consumer places wherever they want (no global DOM manipulation)
• No auto-dismiss — timeouts are the component's responsibility via the exposed hide(id) method
• No HTTP middleware — territory-specific concern, stays local

Package API

const toastService = createToastService(MyToastComponent, 4);
toastService.show({ message: "Saved", variant: "success" });
toastService.hide(id);
// Mount <component :is="toastService.ToastContainerComponent" /> in template

Test plan

• All 8 CI gates pass (format, lint, build, typecheck, lint:pkg, coverage, mutation)
• 15 unit tests covering creation, show, hide, FIFO eviction, maxToasts clamping, onClose, isolation
• 100% line/branch/function/statement coverage
• 90% mutation score (3 equivalent mutants survived — acceptable)

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