Split per-adapter setup into dedicated reference pages under docs/reference/adapters/

[hugocorreia90]

docs/src/content/docs/reference/configuration.md is a single ~1180-line page documenting every adapter inline (DuckDB, Databricks, Snowflake, BigQuery, Fivetran). A user asking "how do I set up Snowflake?" has to scan past four other adapters to find what they need.

Scope

Extract each adapter's auth, environment variable, and warehouse/capacity guidance into a dedicated page under docs/src/content/docs/reference/adapters/<name>.md, cross-linked from the configuration overview. Optionally include a one-table capability matrix (auth methods, supported features per adapter) on the overview page.

This is content reorganization — the existing configuration.md already has the source material. No new technical content needs to be authored.

Code refs

• docs/src/content/docs/reference/configuration.md — source content to split
• docs/astro.config.mjs — sidebar configuration; add a new Adapters group
• New files to create:
  • docs/src/content/docs/reference/adapters/duckdb.md
  • docs/src/content/docs/reference/adapters/databricks.md
  • docs/src/content/docs/reference/adapters/snowflake.md
  • docs/src/content/docs/reference/adapters/bigquery.md
  • docs/src/content/docs/reference/adapters/fivetran.md

Acceptance criteria

• One Markdown page per adapter under reference/adapters/
• Each adapter page covers: auth methods, environment variables, capacity/warehouse settings (whatever applies to that adapter)
• The overview configuration.md is trimmed to high-level structure and links into the per-adapter pages
• The Starlight sidebar (astro.config.mjs) lists the new pages under a coherent group
• npm run build in docs/ succeeds with no broken internal links

Effort

3 hours.