docs: add a navigable Mintlify API reference

[hamedrabah]

Summary

• add a Mintlify docs configuration over the existing repository documentation
• add focused overview and migration quickstart pages
• make the generated sync and async API inventories navigable
• explain the difference between structural API presence and exercised parity evidence

Why

The repository already generates useful API-surface data, but readers currently have to discover large Markdown inventories directly in the tree. This adds a documentation information architecture without replacing the generated sources of truth.

Validation

• ran the official Mintlify CLI validator successfully (mint validate)
• rendered and reviewed the local Mintlify preview, including the generated sync API inventory
• verified every navigation entry resolves to a tracked Markdown or MDX page
• verified docs.json parses as JSON
• ran git diff --check
• reviewed the staged diff for local paths, credentials, and private identifiers

[hamedrabah]

Ready for review — the Mintlify docs now render cleanly in the local preview, and the official mint validate check passes. Would appreciate a maintainer review when you have a chance.

[hamedrabah]

@suchintan, could you review this documentation and parity-map update when convenient? The available automated check is successful and the PR is otherwise waiting for required review.