fix: add AT and ZONE to PostgreSQL SQL keywords for prepareSql

The prepareSql function quotes any word not in SQL_KEYWORDS as an
identifier. Since AT and ZONE were missing from the set, the expression
(NOW() AT TIME ZONE 'UTC') was mangled into (NOW() "AT" TIME "ZONE"
'UTC'), causing INSERT failures on PostgreSQL.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/services/database/postgresql.ts

@@ -339,7 +339,11 @@ const SQL_KEYWORDS = new Set([
   'IF',
   'CURRENT_TIMESTAMP',
   'NOW',
-  'GETDATE'
+  'GETDATE',
+
+  // ==================== Timezone Expression ====================
+  'AT',
+  'ZONE'
 ])
 
 /**

tests/unit/dialects/postgresql-dialect.test.ts

@@ -46,8 +46,8 @@ describe('PostgreSqlDialect', () => {
   })
 
   describe('currentTimestamp', () => {
-    it('should return CURRENT_TIMESTAMP', () => {
+    it('should return explicit UTC timestamp expression', () => {
-      expect(dialect.currentTimestamp()).toBe('CURRENT_TIMESTAMP')
+      expect(dialect.currentTimestamp()).toBe("(NOW() AT TIME ZONE 'UTC')")
     })
   })