[feat] add initial database schema with tables, triggers, and views

database/main/trait_level.sql

@@ -0,0 +1,12 @@
+create table trait_level
+(
+    trait_id INTEGER not null
+        references trait
+            on delete cascade,
+    level    INTEGER not null,
+    ap_cost  INTEGER,
+    label    TEXT,
+    note     TEXT,
+    primary key (trait_id, level)
+);
+