fix(db): add vet_name, result, next_due to healthMigrations ALTER TABLE guards

Existing databases were missing these 3 columns because they were defined
in the CREATE TABLE but not in the healthMigrations array used for
ALTER TABLE on pre-existing DBs. This caused the 'table health_records
has no column named vet_name' error in the Add Health Record modal.

server/db/init.js

@@ -128,7 +128,7 @@ function initDatabase() {
     )
   `);
 
-  // migrate: add OFA-specific columns if missing
+  // migrate: add OFA-specific columns if missing (covers existing DBs)
   const healthMigrations = [
     ['test_type',    'TEXT'],
     ['ofa_result',   'TEXT'],
@@ -136,6 +136,9 @@ function initDatabase() {
     ['performed_by', 'TEXT'],
     ['expires_at',   'TEXT'],
     ['document_url', 'TEXT'],
+    ['result',       'TEXT'],
+    ['vet_name',     'TEXT'],
+    ['next_due',     'TEXT'],
   ];
   for (const [col, def] of healthMigrations) {
     try { db.exec(`ALTER TABLE health_records ADD COLUMN ${col} ${def}`); } catch (_) { /* already exists */ }