Fix and integrate the conanjurer (Conan Exiles) bridge

Fixes the broken, never-loaded conanjurer module and wires it into the bot
following the project convention (cog in *_commands, logic in *_functions).

- conanjurer_functions.py: move 'from __future__' to the top (was a
  SyntaxError on line 6), drop duplicate import; config now comes from
  constants instead of dotenv/.env; guard optional deps (aiomcrcon,
  asyncssh) so the extension loads even when they are absent
- conanjurer_commands.py: single ConanModule(commands.Cog) with the
  standard (bot, logger_name)+setup() shape; owns its RconClient (no more
  undefined bot.cfg/bot.rcon); GM check uses CONAN_GM_ROLE_ID; commands
  report cleanly when RCON is unconfigured
- bot.py: load_extension('conanjurer_commands')
- constants.py: CONAN_* config (env-overridable); integration is dormant
  unless configured
- requirements_bot.txt: add aiomcrcon, asyncssh

Player-join notifications (task 2): watch_players() polls RCON
'listplayers', diffs against the previous set and announces new players on
CONAN_JOIN_CHANNEL_ID. Disabled when that channel is not defined (0).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

bot.py

@@ -71,6 +71,7 @@ async def on_ready():
     await client.load_extension("voice_recognition_commands")
     await client.load_extension("file_search_commands")
     await client.load_extension("latex_commands")
+    await client.load_extension("conanjurer_commands")
     logger.info("Sensors: online")
 
     logger.info(client.cogs)