docs(services): improve Infura tutorials with MetaMask workflow and signing guidance

[rohan911438]

Description

Fixes #1386

This PR refreshes several Services tutorials to provide clearer MetaMask context, improve workflow guidance, and align tutorial structure with existing MetaMask documentation standards.

What Changed

The following tutorials were updated:

• use-web3.js.md
• send-a-transaction-ethers.md
• send-a-transaction-viem.md
• deploy-a-contract-using-web3.js.md
• call-a-contract.md
• layer-2-networks/send-a-transaction.md

Improvements

Added MetaMask Context

Each tutorial now includes a short section explaining:

• Why the workflow is relevant for MetaMask developers.
• The role of MetaMask within the transaction lifecycle.
• When developers should use MetaMask versus direct RPC interactions.

Clarified Signing and Broadcasting

Added standardized guidance describing:

• Transaction signing in MetaMask.
• Transaction broadcasting through Infura endpoints.
• Wallet responsibilities versus provider responsibilities.
• Security considerations around private key management.

Improved Security Guidance

Added warnings before private-key-based examples to clarify that:

• These workflows are intended for local development, testing, or backend automation.
• Production dapps should request signatures through MetaMask or another wallet provider rather than exporting private keys.

Added Recommended MetaMask Workflows

Introduced a MetaMask-first workflow section that explains how developers can:

1. Connect a wallet.
2. Request account access.
3. Sign transactions through MetaMask.
4. Broadcast transactions through the connected provider.

Added Network Selection Guidance

Added notes for tutorials using Sepolia, Polygon, and other EVM networks to help developers:

• Verify the active MetaMask network.
• Confirm endpoint and network alignment.
• Ensure sufficient testnet funds are available before executing examples.

Why

Many tutorials focused primarily on Infura-based workflows and private-key-driven examples without clearly explaining how those workflows fit into a typical MetaMask development experience.

These updates provide a clearer mental model for developers by:

• Explaining wallet and provider responsibilities.
• Promoting safer signing practices.
• Improving consistency across Services tutorials.
• Aligning tutorial content with broader MetaMask documentation patterns.

Testing

• Verified documentation formatting.
• Reviewed Markdown structure for consistency.
• Confirmed updates are content-only and do not affect runtime behavior.

---

Note

Low Risk
Markdown-only documentation with no runtime or API changes; content improves security messaging for developers.

Overview
Six Infura Services Ethereum/Polygon tutorials gain shared MetaMask-oriented prose: relevance for dapp builders, network/RPC alignment checks, a signing vs broadcasting split (wallet signs locally; Infura RPC only), and a wallet-first flow (eth_requestAccounts, injected provider/signer, user confirmation).

Private-key examples (.env, config.ts) are framed with :::warning blocks as local dev, test, or automation only, with production guidance to use in-browser wallet signing instead of exported keys. Tutorial steps and sample scripts are unchanged; updates are markdown-only.

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