Add configurable bot message filtering via DISCORD_ALLOW_BOTS env var:
- 'none' (default): Ignore all other bot messages — matches previous
behavior where only our own bot was filtered, but now ALL bots are
filtered by default for cleaner channels
- 'mentions': Accept bot messages only when they @mention our bot —
useful for bot-to-bot workflows triggered by mentions
- 'all': Accept all bot messages — for setups where bots need to
interact freely
Previously, we only ignored our own bot's messages, allowing all other
bots through. This could cause noisy loops in channels with multiple bots.
8 new tests covering all filter modes and edge cases.
Inspired by openclaw v2026.3.7 Discord allowBots: 'mentions' config.
f8240143b6