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

database/main/species_attribute_mod.sql

@@ -0,0 +1,15 @@
+create table species_attribute_mod
+(
+    species_id   INTEGER not null
+        references species
+            on delete cascade,
+    attribute_id INTEGER not null
+        references attribute
+            on delete restrict,
+    delta        INTEGER not null,
+    primary key (species_id, attribute_id)
+);
+
+create index idx_species_attrmod_attr
+    on species_attribute_mod (attribute_id);
+