Add React Query DevTools and structured query-key factory to prevent cache key collisions

[prodbycorne]

Problem

src/hooks/useSorobanQuery.ts defines query keys as plain string constants (QUERY_KEYS.POOLS, QUERY_KEYS.USER_POSITION). As more queries are added (platform stats, boost config, leaderboard, credits, history) these flat keys will collide — e.g. useUserPosition('pool-a') and useUserPosition('pool-b') both use the key ['userPosition', poolId, publicKey] but if publicKey changes and the old queries are not invalidated correctly, stale data from a previous wallet session can bleed into the new session.

Acceptance Criteria

• src/lib/queryKeys.ts exports a type-safe query key factory using the pattern from TanStack Query docs:

  export const queryKeys = {
    pools: () => ['pools'] as const,
    userPosition: (poolId: string, publicKey: string) => ['userPosition', poolId, publicKey] as const,
    userCredits: (poolId: string, publicKey: string) => ['userCredits', poolId, publicKey] as const,
    platformStats: () => ['platformStats'] as const,
    boostConfig: (poolId: string) => ['boostConfig', poolId] as const,
    leaderboard: (sortKey: string, page: number) => ['leaderboard', sortKey, page] as const,
  }

• All useQuery and queryClient.invalidateQueries call sites in useSorobanQuery.ts switch to this factory
• When publicKey changes in StellarWalletContext, a useEffect calls queryClient.removeQueries({ queryKey: ['userPosition'] }) and queryClient.removeQueries({ queryKey: ['userCredits'] }) so the previous wallet's data is never shown to the next connected wallet
• ReactQueryDevtools imported from @tanstack/react-query-devtools is rendered inside AppShell.tsx only when process.env.NODE_ENV === 'development' (zero bundle cost in production via next/dynamic with ssr: false)
• A Vitest test changes publicKey and verifies the user-scoped cache entries are removed

Relevant Files

• src/lib/queryKeys.ts — create
• src/hooks/useSorobanQuery.ts — migrate to key factory
• src/context/StellarWalletContext.tsx — add queryClient.removeQueries on disconnect
• src/components/AppShell/AppShell.tsx — lazy DevTools

[Oluwasuyi-Timilehin]

Hello maintainers I'm a full stack developer experience in building scalable systems I can handle this perfectly if assigned

[grantfox-oss]

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Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #38)
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