[Extensibility 1/4] refactor: table-driven LLM provider registry - #259

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4, actions/setup-node@v4, actions/upload-artifact@v4, supabase/setup-cli@v1. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

migration returned a non-zero status (already applied?): backend/migrations/20260613_05_workflows_overview_rpc.sql

migration returned a non-zero status (already applied?): backend/migrations/20260613_02_projects_overview_rpc.sql

migration returned a non-zero status (already applied?): backend/migrations/20260602_01_add_document_version_file_metadata.sql

migration returned a non-zero status (already applied?): backend/migrations/20260427_01_move_storage_to_versions.sql

migration returned a non-zero status (already applied?): backend/migrations/20260424_01_docx_version_display_name.sql