refactor(mail): modernize smtp sending with go-mail and unify message gateway pusher

backend/go.mod

@@ -16,8 +16,6 @@ require (
 	github.com/gin-contrib/sessions v1.1.0
 	github.com/gin-gonic/gin v1.12.0
 	github.com/glebarez/sqlite v1.11.0
-	github.com/go-jose/go-jose/v4 v4.1.4
-	github.com/google/go-cmp v0.7.0
 	github.com/google/uuid v1.6.0
 	github.com/gorilla/sessions v1.4.0
 	github.com/gorilla/websocket v1.5.3
@@ -38,6 +36,7 @@ require (
 	github.com/swaggo/swag v1.16.6
 	github.com/tencent-connect/botgo v0.2.1
 	github.com/uptrace/opentelemetry-go-extra/otelzap v0.3.2
+	github.com/wneessen/go-mail v0.8.1
 	go.opentelemetry.io/contrib/instrumentation/github.com/gin-gonic/gin/otelgin v0.70.0
 	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.70.0
 	go.opentelemetry.io/otel v1.45.0
@@ -54,7 +53,6 @@ require (
 	gopkg.in/telebot.v4 v4.0.0-beta.10
 	gorm.io/driver/clickhouse v0.7.0
 	gorm.io/driver/postgres v1.6.2
-	gorm.io/driver/sqlite v1.6.0
 	gorm.io/gorm v1.31.2
 	gorm.io/plugin/dbresolver v1.6.2
 	gorm.io/plugin/opentelemetry v0.1.14
@@ -95,6 +93,7 @@ require (
 	github.com/glebarez/go-sqlite v1.21.2 // indirect
 	github.com/go-faster/city v1.0.1 // indirect
 	github.com/go-faster/errors v0.7.1 // indirect
+	github.com/go-jose/go-jose/v4 v4.1.4 // indirect
 	github.com/go-logr/logr v1.4.4 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
 	github.com/go-openapi/jsonpointer v0.22.1 // indirect
@@ -133,7 +132,6 @@ require (
 	github.com/klauspost/cpuid/v2 v2.4.0 // indirect
 	github.com/leodido/go-urn v1.5.0 // indirect
 	github.com/mattn/go-isatty v0.0.24 // indirect
-	github.com/mattn/go-sqlite3 v1.14.22 // indirect
 	github.com/mfridman/interpolate v0.0.2 // indirect
 	github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
 	github.com/modern-go/reflect2 v1.0.2 // indirect