Include cost estimation in recommended upload workflow

[timfong888]

Problem

wallet costs command exists but isn't in the quick start or recommended workflow. Agents building dApps need programmatic cost estimation, not just CLI output.

Details

• Pricing info ($2.5/TiB/month/copy) is in SKILL.md — good, but no SDK function reference for cost estimation
• The recommended workflow goes straight from wallet init → upload without a cost check step
• For dApps, users expect to see cost before committing to storage

Ask

• Add wallet costs to the quick start flow (between init and upload)
• Document any SDK-level cost estimation APIs
• Show how a dApp would display estimated costs to users before upload