✨ feat: add declarative items to Tabs and derive the active trigger state

[futjesus]

Summary

• Tabs.Trigger without isActive: when omitted, the active styles are derived from Radix's data-state through a named group, so consumers stop mirroring the active value into every trigger. Compute (detail Tabs), kubernetes (cpu/gpu Tabs), settings and billing pages all repeat isActive={activeTab === tab}. Passing isActive still works.
• items: declarative API that renders the list, triggers and contents from an array (value, label, content, optional class names, listClassName). Uncontrolled by default: starts on the first item (or defaultValue) and falls back to the first item when the active one disappears, which compute SizeTabs and kubernetes node pool Tabs implemented locally with useState + useEffect. Passing value keeps the tabs controlled.

Existing children-based usage is unchanged.

Test plan

• New tests: derived active state, items render/switch/onValueChange, defaultValue, fallback when the active item disappears, controlled value, axe
• npx vitest run lib/components/Tabs, lint, types, prettier
• Storybook: Tabs/Light and Dark → DeclarativeItems