Web lib: RPC health and connection status

[0xMegie]

Area: apps/web/src/lib/soroban/health.ts

Goal: Verify RPC health detection drives a stable connection indicator.

Tasks:

• Add MSW handlers for healthy, degraded, and unreachable RPC responses.
• Assert mapped status and user-facing label.
• Test timeout handling with fake timers.

Acceptance:

• No real network and no clock flakiness.
• bun run --cwd apps/web test passes.

[pablowizzy24]

Monitors RPC availability and connection status, helping applications detect issues, maintain reliable blockchain connectivity, and improve user experience.