Improve REP pricing, overflow handling, and modal UX

[KillariDev]

Summary

• Adds a read-only RPC fallback for injected wallet backends so the UI can continue loading data when no wallet provider is available.
• Unifies REP price source labels across overview, collateralization, and liquidation views, with clearer copy for simulation and Uniswap quotes.
• Improves currency rendering with overflow-aware compact formatting and adds coverage for large balance display cases.
• Refines modal headers for better accessibility and layout, including a more usable close control.
• Tightens market question auto-loading and liquidation messaging to better reflect current state and failure reasons.

Testing

• Not run
• Added and updated unit tests covering chain backend behavior, currency formatting/rendering, liquidation modal messaging, market section loading, overview panels, and related hooks/components