[Markets] Build oracle price display for market detail

[samuel2926i39-art]

Summary

Adds OraclePriceWidget for the market detail view, showing the current Pyth-backed reference price and its as-of timestamp, with a visible staleness badge when the feed exceeds a configurable freshness threshold.

Context

• Backed by contracts/predict-iq/src/pyth_client.rs via GET /api/v1/blockchain/oracle/:market_id.
• Before: no oracle price was surfaced on market detail; a stopped feed had no way to be distinguished from a live one.
• After: price + as-of time render together, and a price older than the threshold (default 60s, configurable via prop) shows a Stale badge instead of being presented as current.

Testing

• Manually verified fresh vs. stale states by adjusting freshnessThresholdSeconds against a mocked timestamp.
• Verified error/loading states render distinct, non-misleading UI (no stale price silently shown as fresh).
• No existing test suite wiring for this endpoint yet; component is structured for straightforward unit testing with a mocked fetch.

Closes #1362

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