Document token registry verification and submission requirements

[0xBreadguy]

Summary

The token submission examples omit the verification record now required by megaeth-labs/mega-tokenlist#56, so submissions based on them fail generation even after replacing placeholder addresses. Update the contracts page with valid verification pairs, evidence requirements, and the maintainer attestation at merge.

• Add root-level verification to both illustrative JSON templates and explain all three status/method pairs, including the community default for permissionless factory submissions.

• Explain generated extensions.verification, sourceChain, and sourceAddress, including EVM sources, token-versus-bridge addresses, and absence when no source is recorded.

• Document tokens.megaeth_testnet, separate generated lists from feat: generate separate testnet token list mega-tokenlist#40, and the data-only submission workflow.

• Point all 21 MegaETH Mainnet explorer links on the page to mega.etherscan.io.

Only docs/dev/send-tx/contracts.md changes. Existing tokenlist README examples also need a separate upstream correction; this guide includes the required context directly.

Validation

• Repository-wide Markdown lint and Prettier 3.8.5 checks pass.
• Both JSON templates parse and contain valid status/method pairs; addresses remain explicitly labeled placeholders.
• Relative file links and GitBook block balance checked; git diff --check passes.
• Registry behavior cross-checked against its generator, PR ci: use centralized mega-agents Claude CI actions #56, and submission guidance.
• Repository CI passes on the latest commit, including link, Markdown, formatting, and PR review pipeline checks.
• GitBook has not posted a rendered preview status yet.