Docs - Clean up Invoicing use case page

[MantisClone]

Problem

Invoicing use case page contained AI warnings, marketing fluff, placeholder links, and unverified content that undermined credibility.

Solution Implemented

Cleaned up the Invoicing page following comprehensive cleanup template:

• Removed AI-generated warning box
• Replaced marketing language with benefits-focused, factual copy
• Fixed all placeholder links or added notes about future pages
• Verified all feature claims against request-api codebase
• Updated chain count from 10 to 9 (Fantom deprecated)
• Replaced emoji in title with proper icon property
• Converted Integration Approaches from tabs to card layout (2-col + full-width)
• Reduced Key API Features from 8 to 6 cards for better focus
• Added tooltips for technical terms (IPFS, on-chain, non-custodial)
• Added Check callout after Demo section for better user guidance
• Simplified Quickstart Step 2 wording for clarity

References

• PR feat: Cleanup and improve Invoicing use case page #26: feat: Cleanup and improve Invoicing use case page #26
• Parent issue: Docs - Remove AI slop from Use Case pages #18
• Planning document: /ignore/PLAN_Invoicing_Page.md
• Live page: /use-cases/invoicing.mdx

Status

✅ Complete - Serves as template for remaining use case pages