docs(apps): add Builder Code attribution to migration quickstart config

[bennytimz]

Summary

• Adds ox to the npm install command in Step 1 of the "I'm converting an app" migration path
• Updates the config.ts code block to import Attribution from ox/erc8021, derive a DATA_SUFFIX constant, and pass it as dataSuffix to createConfig — matching the pattern documented in Builder Codes for App Developers
• Appends a sentence to Step 5 (Register on Base.dev) pointing web-traffic users to the Builder Codes guide for transaction attribution outside the Base App browser

Test plan

• Verify the npm install line includes ox between viem and @tanstack/react-query
• Verify the config.ts code block compiles: Attribution.toDataSuffix is a valid export from ox/erc8021 (requires viem ≥ 2.45.0 per the Builder Codes guide)
• Verify highlight={4,6-9,24} correctly marks the new import, DATA_SUFFIX constant, and dataSuffix field
• Verify the lines, expandable, and wrap fence flags are intact
• Verify Step 5 in the "My app has no Farcaster SDK" tab is unchanged
• Verify no other sections of the file were modified

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/2	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 1 Sum 2