📝 task-000: clarify BuffManager duration behavior

[koji-assistant]

Summary

• add BuffManager source module to gettakaro/modules
• document the difference between BuffManager package duration and native 7D2D XML buff duration
• explain that maintenance checks Takaro expiry variables, re-applies active timed buffs, and removes expired ones
• clarify config help text for duration, buff names, maintenance, and the maintenance cronjob

Testing

• npm run build
• node dist/scripts/module-to-json.js modules/BuffManager /tmp/BuffManager-docs-export.json
• verified exported JSON contains the new duration/XML explanation
• model review performed; fixed misleading cooldown/permanent-duration documentation found during review

Runtime game testing not needed for this follow-up because the latest change is documentation/config-help text only.

[koji-assistant]

Follow-up fix from runtime testing feedback:

• duration 0 now creates permanent Takaro tracking (buff_expiry_<package> = 0) so maintenance can keep re-applying it
• /buffplayer, /getbuff, and auto-apply now all create/update tracking variables consistently
• maintenance now gets online PlayerOnGameServer records directly instead of relying on steamId from the game-server player payload, which is safer for 7D2D
• verified with node --check, npm run build, and module export inspection