Fix SQL schema issues across all database engines

- Increase password column from varchar(64) to varchar(255) to
  prevent silent truncation of encrypted passwords
- Add missing UNIQUE constraint on iid in MySQL
- Add missing IX_ident_switch_iid index in PostgreSQL
- Remove deprecated int display width in MySQL (int(10) -> int)
- Fix trailing comma syntax error in SQLite 2018121800 migration
- Normalize indentation across all initial SQL files
- Add migration 2026021000 for all engines to fix existing installs

SQL/sqlite/2026021000.sql

@@ -0,0 +1,75 @@
+PRAGMA foreign_keys=off;
+BEGIN TRANSACTION;
+
+ALTER TABLE ident_switch RENAME TO ident_switch_old;
+
+CREATE TABLE ident_switch
+(
+	id
+		integer
+		PRIMARY KEY,
+	user_id
+		integer
+		NOT NULL
+		REFERENCES users(user_id) ON DELETE CASCADE ON UPDATE CASCADE,
+	iid
+		integer
+		NOT NULL
+		REFERENCES identities(identity_id) ON DELETE CASCADE ON UPDATE CASCADE
+		UNIQUE,
+	username
+		varchar(64),
+	password
+		varchar(255),
+	imap_host
+		varchar(64),
+	imap_port
+		integer
+		CHECK(imap_port > 0 AND imap_port <= 65535),
+	imap_delimiter
+		char(1),
+	label
+		varchar(32),
+	flags
+		integer
+		NOT NULL
+		DEFAULT(0),
+	smtp_host
+		varchar(64),
+	smtp_port
+		integer
+		CHECK(smtp_port > 0 AND smtp_port <= 65535),
+	smtp_auth
+		smallint
+		NOT NULL
+		DEFAULT 1,
+	drafts_mbox
+		varchar(64),
+	sent_mbox
+		varchar(64),
+	junk_mbox
+		varchar(64),
+	trash_mbox
+		varchar(64),
+	UNIQUE (user_id, label)
+);
+CREATE INDEX IX_ident_switch_user_id ON ident_switch(user_id);
+CREATE INDEX IX_ident_switch_iid ON ident_switch(iid);
+
+INSERT OR ROLLBACK INTO
+	ident_switch (
+		id, user_id, iid, username, password, imap_host, imap_port,
+		imap_delimiter, label, flags, smtp_host, smtp_port, smtp_auth,
+		drafts_mbox, sent_mbox, junk_mbox, trash_mbox
+	)
+SELECT
+	id, user_id, iid, username, password, imap_host, imap_port,
+	imap_delimiter, label, flags, smtp_host, smtp_port, smtp_auth,
+	drafts_mbox, sent_mbox, junk_mbox, trash_mbox
+FROM
+	ident_switch_old;
+
+DROP TABLE ident_switch_old;
+
+COMMIT;
+PRAGMA foreign_keys=on;