feat: add GenTech Labs as registered x402 facilitator with examples

[ProtoJay4789]

Adds GenTech Labs (gentechlabs.net) as a known x402 facilitator in the X402ActionProvider, enabling agents to discover and use GenTech's 16+ paid API endpoints covering gaming, DeFi, NFTs, security, and wallet analytics.

Changes

1. constants.ts: Added gentech to KNOWN_FACILITATORS registry pointing to https://api.gentechlabs.net
2. README.md: Added GenTech integration example section with preregistration, discovery, and usage examples

Example Usage

Agents can now discover and use GenTech services via:

// Discover GenTech services
discover_x402_services({ facilitator: "gentech", keyword: "games" })

// Search games with x402 payment
make_http_request({ url: "https://api.gentechlabs.net/v1/games/search", queryParams: { q: "Elden Ring" } })
retry_http_request_with_x402({ url: "...", selectedPaymentOption: {...} })

This builds on the existing x402 Action Provider infrastructure added in #1021 and continues the x402 ecosystem expansion.

[cb-heimdall]

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