refactor: add table primitive and migrations by date; feat: add mcp connectors

backend/migrations/20260602_04_drop_documents_filename.sql

@@ -0,0 +1,27 @@
+-- Migration date: 2026-06-02
+
+-- Migration: remove legacy document-level filename.
+--
+-- Before dropping the old column, copy any remaining legacy names onto
+-- version rows that do not yet have their own filename/display value.
+-- A later migration renames document_versions.display_name to filename.
+
+DO $$
+BEGIN
+  IF EXISTS (
+    SELECT 1
+    FROM information_schema.columns
+    WHERE table_schema = 'public'
+      AND table_name = 'documents'
+      AND column_name = 'filename'
+  ) THEN
+    UPDATE public.document_versions dv
+    SET display_name = d.filename
+    FROM public.documents d
+    WHERE dv.document_id = d.id
+      AND (dv.display_name IS NULL OR btrim(dv.display_name) = '');
+
+    ALTER TABLE public.documents
+      DROP COLUMN filename;
+  END IF;
+END $$;