Add background mail checking and new mail notifications

SQL/sqlite/2026021002.sql

@@ -0,0 +1,25 @@
+ALTER TABLE ident_switch
+	ADD notify_check
+		smallint
+		NOT NULL
+		DEFAULT 1;
+
+ALTER TABLE ident_switch
+	ADD notify_basic
+		smallint
+		DEFAULT NULL;
+
+ALTER TABLE ident_switch
+	ADD notify_sound
+		smallint
+		DEFAULT NULL;
+
+ALTER TABLE ident_switch
+	ADD notify_desktop
+		smallint
+		DEFAULT NULL;
+
+ALTER TABLE ident_switch
+	ADD notify_sound_url
+		varchar(255)
+		DEFAULT NULL;