Soroban event decoder framework (#23) + high-density FleetGrid layout (#18)

[KarenZita01]

Closes #23, Closes #18

Issue #23 — Real-Time In-App Soroban Log Events Decoding Framework

\\src/hooks/useContractEvents.ts\\

• Properly parses Soroban RPC WebSocket events with base64 XDR topic/value decoding
• Supports three networks (testnet, futurenet, mainnet) via
  etwork\ parameter
• 6 event decoders: meter_reading, balance_low, tariff_update, unauthorized_access, device_fault, pricing_update
• Auto-reconnect with 3s delay, FIFO buffer capped at 200 events
• Exposes { events, latestBlock }\

Issue #18 — High-Density Layout Visualizers for Fleet Asset Managers

\\src/components/spatial/FleetGrid.tsx\\

• Responsive CSS Grid (\grid-cols-2 sm:grid-cols-3 md:grid-cols-4 lg:grid-cols-6)
• Asset cards with name (truncated), status dot (green/red/yellow), grid ID, uptime %, resource bar with color gradient, relative last-ping time
• Filter controls (All, Online, Offline, Maintenance) with active highlighting
• Search input (case-insensitive substring match)
• \content-visibility: auto\ for large asset sets