Refactor documentation structure and dependencies for migration to Fumadocs

- Updated `.gitignore` to include new build and generated content directories.
- Removed outdated Mintlify configuration files and documentation.
- Introduced new `MIGRATION.md` to outline the transition from Mintlify to Fumadocs.
- Added `mdx-components.tsx` for MDX component configuration and compatibility.
- Updated `package.json` and `next.config.mjs` for new dependencies and Next.js configuration.
- Created `source.config.ts` for content source configuration.
- Added OpenAPI specification in `openapi.json` for API documentation.
- Removed legacy files and adjusted project structure to align with Fumadocs conventions.

docs/scripts/generate-openapi.ts

@@ -0,0 +1,10 @@
+import { generateFiles } from 'fumadocs-openapi';
+import { openapi } from '../lib/openapi';
+
+await generateFiles({
+  input: openapi,
+  output: 'content/docs/api-reference',
+  groupBy: 'tag',
+});
+
+console.log('✓ OpenAPI documentation generated in content/docs/api-reference/');