Preview multiple Scan OpenAPI servers

[danielporterda]

Summary

• preview PR built from the Transform Scan OpenAPI server URL #651 branch so the hosted Mintlify deployment shows the full Scan OpenAPI transform plus multiple server entries
• expands the Scan OpenAPI server transform from one MainNet Scan host to the ten MainNet Scan hosts already listed in the Splice docs
• regenerates scan.yaml and scan-stream-server.yaml so the hosted preview can show whether Mintlify renders a server dropdown or otherwise changes the curl examples

This is intentionally a preview PR, not the narrow fix proposed in #651.

Preview target

Once the Mintlify preview deploys, inspect:

• /reference/splice-scan-api/external/v0scans
• /reference/splice-scan-streaming-api/pre-alpha/bulkstoragedownload

Screenshots

Pending Mintlify preview deployment. This PR exists specifically to generate the hosted preview for the multi-host rendering decision.

Validation

• direnv exec . npm run generate:splice-mintlify-openapi
• direnv exec . python3 -m pytest tests/test_splice_mintlify_openapi.py
• direnv exec . python3 -m py_compile scripts/generate_splice_mintlify_openapi.py
• direnv exec . npm run validate:splice-mintlify-openapi-nav
• git diff --check