[Task](shares): Migrate `shares/item.jsx`

[hodanoori]

Task Description

Convert ShareItem from a class component to a functional TypeScript component. The component renders a single share table row with polling logic to reload pending shares every 5 seconds, a RuleTooltip inner class component for displaying access rules, and dependency loading for share rules via loadShareRulesOnce. It uses componentDidMount, UNSAFE_componentWillReceiveProps, and componentWillUnmount to manage polling and rule loading lifecycle.

Acceptance Criteria

• Test file item.test.tsx created with 18 unit tests covering: row rendering, share network display, access rules display, dependency loading (loadShareRulesOnce called on mount), polling starts for pending shares, polling stops when share becomes available, polling cleans up on unmount
• All tests pass (pnpm vitest run)
• File renamed to item.tsx with TypeScript interfaces defined for Rule, ShareRulesState, Share, ShareNetwork, and ShareItemProps
• componentDidMount + UNSAFE_componentWillReceiveProps + componentWillUnmount replaced with useEffect hooks
• Polling managed via useRef for the interval ID, reacting to share.status
• startPolling and stopPolling methods converted to inline effect logic
• Inner RuleTooltip class component converted to a functional component
• loadShareRulesOnce called in a separate useEffect reacting to share.id
• No TypeScript errors (pnpm typecheck), no lint errors (pnpm lint)
• Manual visual testing: share rows render correctly, pending shares poll and update, access rules tooltip displays