docs: add Supabase setup guide to project connection page

[mintlify]

Adds a dedicated Supabase section to the project connection page, since Supabase runs on Postgres and customers were unsure whether it's supported.

Changes to get-started/setup-lightdash/connect-project.mdx:

• New "Supabase" card in the warehouse list at the top of the page
• Tip on the Postgres section pointing Supabase users at the new section
• New ### Supabase section covering:
  • Mapping Supabase Session Pooler parameters → Lightdash Postgres connection fields
  • Two setup tabs:
    • Quickstart repo — full walkthrough of lightdash/lightdash-supabase-quickstart (CLI install, AI skills, Supabase MCP, setup/set-warehouse scripts, AI-generated models)
    • Manual setup in the UI — short steps using the existing Postgres form
  • Troubleshooting table for common Supabase-specific issues (pooler user format, Network Restrictions, SSL)

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Requested by: ian@lightdash.com via Slack
Mintlify session: slack_1782742593.540899_C0AM8D5UUR5

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