docs(v2): add Examples showcase section
Surface the ready-to-run configs under examples/ in the v2 docs. Adds a new Examples section with a how-to-run intro (run from the example dir), a companion-files/setup guide, categorized index tables linking each example to GitHub with a Setup column, and three inlined end-to-end recipes. Cross-linked from the introduction page. Excludes examples/pool_metadata (references the removed Deno filter) and examples/_deprecated. Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>