feat: add welcome message functionality

- Introduced a new welcome service and repository for managing welcome messages, channels, and GIFs.
- Added commands to set welcome channel, message, DM, and GIF through the bot's configuration.
- Implemented event handling for new guild members to send welcome messages and DMs based on configuration.
- Updated main application to include the new welcome service in the bot's services.

internal/bot/bot.go

@@ -30,9 +30,11 @@ func NewBot(token, appID, guildID, lavalinkHost, lavalinkPass string, cmds []*di
 	// Intents needed for:
 	// - InteractionCreate (slash commands): Guilds
 	// - MessageCreate (leveling): GuildMessages
+	// - GuildMemberAdd (welcome messages): GuildMembers
 	// - VoiceStateUpdate (meeting lobby): GuildVoiceStates
 	// - MessageReactionAdd (scheduling via reactions): GuildMessageReactions + DirectMessageReactions
 	session.Identify.Intents = discordgo.IntentsGuilds |
+		discordgo.IntentsGuildMembers |
 		discordgo.IntentsGuildMessages |
 		discordgo.IntentsGuildVoiceStates |
 		discordgo.IntentsGuildMessageReactions |
@@ -73,6 +75,10 @@ func (b *Bot) Start() error {
 		events.HandleMessageCreate(s, m, b.Services)
 	})
 
+	b.Session.AddHandler(func(s *discordgo.Session, m *discordgo.GuildMemberAdd) {
+		events.HandleGuildMemberAdd(s, m, b.Services)
+	})
+
 	b.Session.AddHandler(func(s *discordgo.Session, vs *discordgo.VoiceStateUpdate) {
 		events.HandleVoiceStateUpdate(s, vs, b.Services)
 		music.OnVoiceStateUpdate(vs)