Implement graceful degradation for oracle price unavailability

[abayomicornelius]

Problem

If keeper fails to submit prices, all trading halts immediately with no fallback.

Why it matters

Single point of failure in price feeds risks total platform unavailability.

Suggested fix

Add fallback to last known good price with staleness warning after reasonable timeout.

Acceptance criteria

• Define max price staleness threshold
• Use last good price as fallback
• Emit staleness warning event
• Test degraded mode operations

[skaichima]

@skaichima has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hello, I’d be happy to take this on. I’ll implement a configurable staleness threshold with last-known-good price fallback and emit a clear warning event when prices become stale. I’ll also add tests covering keeper failures and degraded-mode trading to ensure the fallback behaves safely without disrupting normal price updates. ETD is in 6 hours tops, please assign

ℹ️ Repo Maintainers: To accept this application, review their application or assign @skaichima to this issue.