feat(contract): Reflector oracle cross-asset sanity checks (D12)

[cybermax4200]

Summary

Adds a Reflector oracle divergence guard to the blend_leverage strategy. Before executing a deposit or rebalance, the contract fetches prices from both Blend's internal oracle and Reflector and refuses if they diverge beyond a configurable threshold.

Changes

oracle.rs (new)

• OracleClient — single contractclient trait covering both Blend's oracle and Reflector (same interface)
• assert_price_aligned(e, config) — fetches both prices, normalises to 1e7, computes divergence in bps, emits oracle/diverge event and returns ExternalError on failure
• normalise_to_7(price, decimals) — converts any decimal precision to Blend's 1e7 scale
• Staleness check: prices older than 300s are treated as downtime

storage.rs

• Config gains reflector: Option<Address> and oracle_threshold: i128
• None reflector disables the guard (backward compatible)

lib.rs

• Constructor parses args[8] (reflector, optional) and args[9] (threshold bps, default 200)
• deposit() calls oracle::assert_price_aligned before any pool interaction
• rebalance() calls oracle::assert_price_aligned after the debt check

Tests (oracle::tests)

• test_no_oracle_configured_passes — guard disabled when reflector is None
• test_aligned_divergence_zero — 0 bps divergence passes
• test_diverging_prices_exceed_threshold — 500 bps > 200 bps threshold refused
• test_divergence_at_threshold_passes — exactly at threshold passes (not strictly greater)
• test_oracle_downtime_returns_none — None response refused
• test_stale_price_detected — price older than 300s refused
• test_normalise_* — 14→7, 7→7, 4→7 decimal conversions

Closes #53

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[Dgetsylver]

Thanks — this is valuable (oracle divergence guard). It isn't on main and conflicts with current contract code — could you rebase onto latest main? (security feature, keen to land it)