fix(reserves): classify USDC/OUSG direct treasuries as very-low risk

Migration script used 'treasury' pattern which doesn't match
'treasuries' (different suffix). Fix 2 slices that were missed:
- USDC: U.S. Treasuries 75% (low → very-low)
- OUSG: Short-Term U.S. Treasuries 80% (low → very-low)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: TokenBrice

src/lib/stablecoins.ts

@@ -109,7 +109,7 @@ export const TRACKED_STABLECOINS: StablecoinMeta[] = [
       ],
     },
     reserves: [
-      { name: "U.S. Treasuries", pct: 75, risk: "low" },
+      { name: "U.S. Treasuries", pct: 75, risk: "very-low" },
       { name: "Overnight Repos", pct: 18, risk: "very-low" },
       { name: "Cash Deposits", pct: 7, risk: "very-low" },
     ],
@@ -352,7 +352,7 @@ export const TRACKED_STABLECOINS: StablecoinMeta[] = [
     ],
     reserves: [
       // Source: Ondo Finance docs + Ankura Trust daily reports. Ondo targets 99%+ Treasuries; 104% overcollateralized.
-      { name: "Short-Term U.S. Treasuries", pct: 80, risk: "low" },
+      { name: "Short-Term U.S. Treasuries", pct: 80, risk: "very-low" },
       { name: "iShares Short Treasury Bond ETF", pct: 15, risk: "very-low" },
       { name: "Bank Demand Deposits", pct: 5, risk: "very-low" },
     ],