feat(group): refactor group invite workflow for improved user experience

- Simplify InviteMembers to always send invite card directly to invitee
- Modify RespondInvite to check group join type (anyone vs need approval) before adding member
- Update SetGroupAddRequest to properly handle invite flow with invitee agreement and admin approval stages
- Add case-insensitive search using LOWER() in user repository
- Add random offset (0-50) for first page of recommended posts
- Update dependencies: remove gorilla/websocket, promote gomail to direct dependency

go.mod

@@ -7,7 +7,6 @@ require (
 	github.com/gin-gonic/gin v1.9.1
 	github.com/golang-jwt/jwt/v5 v5.2.0
 	github.com/google/uuid v1.5.0
-	github.com/gorilla/websocket v1.5.3
 	github.com/gorse-io/gorse-go v0.5.0-alpha.3
 	github.com/minio/minio-go/v7 v7.0.66
 	github.com/redis/go-redis/v9 v9.3.1
@@ -18,6 +17,7 @@ require (
 	gorm.io/driver/postgres v1.5.4
 	gorm.io/driver/sqlite v1.5.4
 	gorm.io/gorm v1.25.5
+	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df
 )
 
 require (
@@ -80,7 +80,6 @@ require (
 	golang.org/x/text v0.22.0 // indirect
 	google.golang.org/protobuf v1.31.0 // indirect
 	gopkg.in/alexcesaro/quotedprintable.v3 v3.0.0-20150716171945-2caba252f4dc // indirect
-	gopkg.in/gomail.v2 v2.0.0-20160411212932-81ebce5c23df // indirect
 	gopkg.in/ini.v1 v1.67.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )