feat(documents): prepare inbox suggestions and add entity assignments

backend/db/migrations/0077_scanner_inbox_preparation.sql

@@ -0,0 +1,13 @@
+ALTER TABLE "scanner_inbox_documents"
+    ADD COLUMN "suggestion_status" text NOT NULL DEFAULT 'pending',
+    ADD COLUMN "suggestion" jsonb,
+    ADD COLUMN "suggestion_message" text,
+    ADD COLUMN "suggestion_claim" uuid,
+    ADD COLUMN "suggestion_updated_at" timestamptz NOT NULL DEFAULT now();
+--> statement-breakpoint
+ALTER TABLE "scanner_inbox_documents" ADD CONSTRAINT "scanner_inbox_suggestion_status_check"
+    CHECK ("suggestion_status" IN ('pending', 'processing', 'ready', 'failed'));
+--> statement-breakpoint
+CREATE INDEX "scanner_inbox_suggestion_queue_idx"
+    ON "scanner_inbox_documents" ("suggestion_status", "suggestion_updated_at", "received_at")
+    WHERE "filed_at" IS NULL;