Docs - Convert BlockScout integration guide from Notion to published docs

[MantisClone]

Problem

The BlockScout integration guide was written as a Notion page (public-issues#164, Done). It's not discoverable by external integrators since it lives in Notion rather than our published documentation site.

As we onboard more integrators (Marco/FT Web, others requesting redirect), this guide should be the canonical reference for how to integrate with the Request Network secure payment page.

Proposed Solution

Migrate the BlockScout integration guide content from Notion into mintlify-docs as a proper documentation page. This should cover:

• Client ID setup and authentication
• Creating payment requests via API
• Secure payment page integration (embedding, redirect)
• Webhook configuration for payment status updates

Generalize where possible so it serves as the integration guide for all orchestrators, not just BlockScout.

Considerations

• The Notion guide may reference BlockScout-specific details — generalize these into an "Orchestrator Integration Guide"
• Related to mintlify-docs#47 (make beta docs good enough to replace legacy docs)
• Redirect URL configuration (private-issues#265) will need to be documented once implemented
• Original Notion guide: created as part of public-issues#164

[MantisClone]

Closing as duplicate of #81 (Pay-in integration guide). The BlockScout guide is essentially a pay-in integration guide — the general guide (#81) should incorporate the BlockScout-specific content rather than maintaining two separate docs. Consolidating into #81.