Docs mintlify improvements (cube-js#10577)

* docs(mintlify): Migrate to docs.json, reorganize tabs and sections

- Upgrade from deprecated mint.json to docs.json format
- Add banner announcing preview status with link to live docs
- Add style.css for full-width tables
- Reorder tabs: Documentation, Admin, Embedding, API Reference, Cube Core, Access & Security
- Move Configuration and SSO/Users sections to Admin tab
- Populate Cube Core tab with dedicated files (getting started, deployment, config, auth, migration)
- Remove Cube Core groups from Documentation tab to avoid duplication
- Move Access Policies page to Documentation > Data Modeling
- Fix component transform to handle alert boxes with attributes (heading=)
- Delete old mint.json

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* docs(mintlify): improve navigation structure and page descriptions

- Remove duplicate Configuration group from Admin tab
- Move API Recipes to Cube Core tab
- Move MCP Server to Documentation > Integrations
- Rename API Reference tab to Reference and add Configuration Reference
- Rename first Admin group to Data Sources
- Move Access Control under Documentation > Data Modeling
- Remove unused pages from Access & Security tab
- Remove Snowflake/Databricks getting started groups temporarily
- Add sidebarTitle overrides for index pages (SSO, Access Control)
- Replace 200+ copied/truncated page descriptions with unique one-sentence summaries

Made-with: Cursor

* docs(mintlify): add sidebar overrides and remove redundant pages

- Remove api-reference index page from Core Data APIs group
- Add sidebarTitle: Overview to Core Data APIs and Embed APIs index pages
- Use explicit /index paths for proper frontmatter resolution

Made-with: Cursor

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: keydunov