KI-AGENT: Persistente App-Sessions mit Refresh-Tokens ergänzen

backend/db/migrations/0056_auth_refresh_tokens.sql

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+CREATE TABLE IF NOT EXISTS "auth_refresh_tokens" (
+    "id" uuid PRIMARY KEY DEFAULT gen_random_uuid() NOT NULL,
+    "user_id" uuid NOT NULL,
+    "tenant_id" bigint,
+    "token_hash" text NOT NULL,
+    "created_at" timestamp with time zone DEFAULT now() NOT NULL,
+    "expires_at" timestamp with time zone NOT NULL,
+    "revoked_at" timestamp with time zone,
+    CONSTRAINT "auth_refresh_tokens_token_hash_unique" UNIQUE("token_hash"),
+    CONSTRAINT "auth_refresh_tokens_user_id_auth_users_id_fk"
+        FOREIGN KEY ("user_id") REFERENCES "public"."auth_users"("id")
+        ON DELETE cascade ON UPDATE cascade,
+    CONSTRAINT "auth_refresh_tokens_tenant_id_tenants_id_fk"
+        FOREIGN KEY ("tenant_id") REFERENCES "public"."tenants"("id")
+        ON DELETE set null ON UPDATE cascade
+);
+
+CREATE INDEX IF NOT EXISTS "auth_refresh_tokens_user_id_idx"
+    ON "auth_refresh_tokens" ("user_id");
+CREATE INDEX IF NOT EXISTS "auth_refresh_tokens_expires_at_idx"
+    ON "auth_refresh_tokens" ("expires_at");