[feat] extend database schema with new tables and indexes

database/main/shield.sql

@@ -0,0 +1,17 @@
+create table shield
+(
+    id              INTEGER
+        primary key,
+    item_id         INTEGER not null
+        unique
+        references item
+            on delete cascade,
+    kampftechnik_id INTEGER not null
+        references kampftechnik
+            on delete restrict,
+    at_mod          INTEGER default 0,
+    pa_mod          INTEGER default 0,
+    zusatz_rs       INTEGER default 0,
+    zusatz_be       REAL    default 0
+);
+