feat(db): RESTRICT vocabulary deletes; non-empty label/lang constraints

crates/db/migrations/0002_vocabularies_authorities.sql

@@ -6,15 +6,15 @@ CREATE TABLE vocabulary (
 
 CREATE TABLE term (
     id            UUID PRIMARY KEY,
-    vocabulary_id UUID NOT NULL REFERENCES vocabulary (id) ON DELETE CASCADE,
+    vocabulary_id UUID NOT NULL REFERENCES vocabulary (id) ON DELETE RESTRICT,
     external_uri  TEXT                 -- e.g. Getty AAT / KulturNav / Wikidata URI
 );
 CREATE INDEX term_vocabulary_idx ON term (vocabulary_id);
 
 CREATE TABLE term_label (
     term_id UUID NOT NULL REFERENCES term (id) ON DELETE CASCADE,
-    lang    TEXT NOT NULL,            -- BCP-47, e.g. 'sv', 'en'
-    label   TEXT NOT NULL,
+    lang    TEXT NOT NULL CHECK (lang <> ''),
+    label   TEXT NOT NULL CHECK (label <> ''),
     PRIMARY KEY (term_id, lang)
 );
 
@@ -28,7 +28,7 @@ CREATE INDEX authority_kind_idx ON authority (kind);
 
 CREATE TABLE authority_label (
     authority_id UUID NOT NULL REFERENCES authority (id) ON DELETE CASCADE,
-    lang         TEXT NOT NULL,
-    label        TEXT NOT NULL,
+    lang         TEXT NOT NULL CHECK (lang <> ''),
+    label        TEXT NOT NULL CHECK (label <> ''),
     PRIMARY KEY (authority_id, lang)
 );