Update worldchain URLs to the ones in worldchain domain.

[piohei]

Update worldchain URLs to the ones in worldchain domain.

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Note

Low Risk
Configuration-only URL swaps for dev/CI/test defaults; no application logic or auth changes.

Overview
Replaces default World Chain RPC endpoints from Alchemy public URLs with the official worldcoin.org RPC hosts for mainnet and Sepolia.

Updates are limited to defaults and examples: .env.example, CI test job fallbacks when secrets are unset (WORLDCHAIN_RPC_URL / WORLDCHAIN_SEPOLIA_RPC_URL), DEFAULT_WORLDCHAIN_RPC_URL in walletkit-testkit, and the Anvil fork fallback in the authenticator integration test. Secret overrides in CI behavior are unchanged—only the public fallback URLs differ.

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