docs: add Stellar explorer recipes

[kaycke1337]

Summary

• Add guides/stellar-explorer-recipes.mdx with stellar.expert URL patterns for accounts, transactions, contracts, and assets.
• Include a copy-paste TypeScript stellarExplorerUrl helper and UX/a11y guidance for explorer links.
• Clarify stealth-account explorer privacy and add alternative explorer notes.
• Link the page from the SDK Stellar page, the stealth payments guide, and the guides navigation.

Validation

• npx --yes prettier@3.4.0 --check docs.json guides/stellar-explorer-recipes.mdx guides/stealth-payments.mdx sdk/chains/stellar.mdx
• node -e "JSON.parse(require(\"fs\").readFileSync(\"docs.json\",\"utf8\")); console.log(\"docs.json ok\")"

Note: this repo does not currently contain guides/stellar-quickstart.mdx, so I linked the new page from guides/stealth-payments.mdx as the closest Stellar-oriented guide.

Closes #12.

[truthixify]

Heads up — we've just set up a develop branch as the integration target for all Drips × Stellar Wave contributions, and I've retargeted this PR's base from main to develop on your behalf. The diff is unchanged; nothing to do on your end.

Going forward, please branch from and target develop. We'll periodically merge develop → main as we cut releases. Thanks for contributing!