Add custom auth, connection testing, preconfig_only, and security fixes

Major form improvements:
- Custom SMTP/Sieve credentials (separate username/password per protocol)
- Connection testing on save (IMAP, SMTP, Sieve) with localized errors
- preconfig_only mode to restrict domains to preconfigured entries
- Form POST value preservation on save errors (auth selects, passwords)
- Smart host placeholders (SMTP/Sieve default to IMAP host)

Security and bug:
- Fix password re-encryption bug (was comparing raw vs encrypted values)
- Fix XSS: escape label output in special folders form
- Fix parse_url() return value not checked for false
- Fix decrypt() failures not handled (fallback to empty string)
- Sanitize log output (remove raw POST data from log messages)
- Replace weak == comparisons with strict === (PHP and JS)

SQL changes:
- Consolidate 4 migrations (2026021000-03) into single 2026021000
- Remove now unused notify_sound_url column
- Add smtp_username, smtp_password, sieve_username, sieve_password columns

SQL/mysql/2026021000.sql

@@ -1,5 +1,76 @@
+-- Upgrade from v4.x to v5.x
+-- Increase password column for encrypted values
 ALTER TABLE `ident_switch`
 	MODIFY `password` varchar(255);
 
+-- Add unique constraint on identity ID
 ALTER TABLE `ident_switch`
 	ADD UNIQUE (`iid`);
+
+-- Add Sieve support
+ALTER TABLE `ident_switch`
+	ADD `sieve_host` varchar(64) AFTER `smtp_auth`;
+
+ALTER TABLE `ident_switch`
+	ADD `sieve_port`
+		int
+		CHECK(`sieve_port` > 0 AND `sieve_port` <= 65535)
+		AFTER `sieve_host`;
+
+ALTER TABLE `ident_switch`
+	ADD `sieve_auth`
+		smallint
+		NOT NULL
+		DEFAULT 1
+		AFTER `sieve_port`;
+
+-- Add custom SMTP/Sieve credentials
+ALTER TABLE `ident_switch`
+	ADD `smtp_username`
+		varchar(64)
+		DEFAULT NULL
+		AFTER `smtp_auth`;
+
+ALTER TABLE `ident_switch`
+	ADD `smtp_password`
+		varchar(255)
+		DEFAULT NULL
+		AFTER `smtp_username`;
+
+ALTER TABLE `ident_switch`
+	ADD `sieve_username`
+		varchar(64)
+		DEFAULT NULL
+		AFTER `sieve_auth`;
+
+ALTER TABLE `ident_switch`
+	ADD `sieve_password`
+		varchar(255)
+		DEFAULT NULL
+		AFTER `sieve_username`;
+
+-- Add notification settings
+ALTER TABLE `ident_switch`
+	ADD `notify_check`
+		smallint
+		NOT NULL
+		DEFAULT 1
+		AFTER `sieve_password`;
+
+ALTER TABLE `ident_switch`
+	ADD `notify_basic`
+		smallint
+		DEFAULT NULL
+		AFTER `notify_check`;
+
+ALTER TABLE `ident_switch`
+	ADD `notify_sound`
+		smallint
+		DEFAULT NULL
+		AFTER `notify_basic`;
+
+ALTER TABLE `ident_switch`
+	ADD `notify_desktop`
+		smallint
+		DEFAULT NULL
+		AFTER `notify_sound`;

SQL/mysql/2026021001.sql

@@ -1,15 +0,0 @@
-ALTER TABLE `ident_switch`
-	ADD `sieve_host` varchar(64) AFTER `smtp_auth`;
-
-ALTER TABLE `ident_switch`
-	ADD `sieve_port`
-		int
-		CHECK(`sieve_port` > 0 AND `sieve_port` <= 65535)
-		AFTER `sieve_host`;
-
-ALTER TABLE `ident_switch`
-	ADD `sieve_auth`
-		smallint
-		NOT NULL
-		DEFAULT 1
-		AFTER `sieve_port`;

SQL/mysql/2026021002.sql

@@ -1,30 +0,0 @@
-ALTER TABLE `ident_switch`
-	ADD `notify_check`
-		smallint
-		NOT NULL
-		DEFAULT 1
-		AFTER `sieve_auth`;
-
-ALTER TABLE `ident_switch`
-	ADD `notify_basic`
-		smallint
-		DEFAULT NULL
-		AFTER `notify_check`;
-
-ALTER TABLE `ident_switch`
-	ADD `notify_sound`
-		smallint
-		DEFAULT NULL
-		AFTER `notify_basic`;
-
-ALTER TABLE `ident_switch`
-	ADD `notify_desktop`
-		smallint
-		DEFAULT NULL
-		AFTER `notify_sound`;
-
-ALTER TABLE `ident_switch`
-	ADD `notify_sound_url`
-		varchar(255)
-		DEFAULT NULL
-		AFTER `notify_desktop`;