feat(proxy): price proxied calls per HTTP method

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Closes #1226

Summary

Adds optional price_per_method_usdc?: Partial<Record<HttpMethod, string>> to ApiDefinition (src/types/gateway.ts), adds resolveMethodPriceUsdc(api, method) and getMethodPriceUsdc(slugOrId, method) in src/data/apiRegistry.ts (normalizing method names case-insensitively and falling back to price_per_call_usdc), and updates handleProxy (src/routes/proxyRoutes.ts) to resolve the price for req.method when deducting credits and recording usage events.

Acceptance Criteria Mapping

• An API with price_per_method_usdc: { GET: "0.005", POST: "0.02" } charges 0.005 on GET and 0.02 on POST: Verified in src/data/apiRegistry.test.ts and src/routes/gatewayRoutes.test.ts.
• An HTTP method not listed in price_per_method_usdc charges price_per_call_usdc: Verified via PUT fallback in both unit and route tests.
• Method lookup is case-insensitive: Normalized via method.trim().toUpperCase().
• Usage events record the method-specific price: usageStore.record receives amountCharged: priceUsdc.

Validation

• npx jest src/data/apiRegistry.test.ts src/routes/gatewayRoutes.test.ts --no-cache (all pass).

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Payout Wallet (Base Mainnet USDC / EVM): 0x3806cd592a508d1992Ed007C2F53de251C2E7452