feat: modmail ticket system with Components V2 + HTML transcripts

- DM-based modmail: user DMs bot -> ticket channel created
- Staff relay: messages in ticket -> DM to user
- Configurable categories via /modmail addcategory
- Setup via /modmail setup (category, staff role, log channel)
- Close command: /close or !close -> HTML transcript generated
- Components V2: Container, TextDisplay, Separator, persistent views
- Transcript: dark theme HTML with staff badges, avatars, timestamps

bot.py

@@ -25,6 +25,7 @@ class VisionBot(commands.Bot):
     async def setup_hook(self):
         logger.info("Chargement des cogs...")
         await self.load_extension("commandes.hello")
+        await self.load_extension("commandes.modmail")
 
         if config.DEV and DEV_GUILD_IDS:
             logger.info(f"Mode DEV — sync des commands sur les guilds: {DEV_GUILD_IDS}")