Initial bridge: Discord <-> Fluxer channel relay via webhooks

- discord.py + fluxer.py bots run side-by-side in one asyncio process
- messages relay through per-channel incoming webhooks with the original
  author's name and avatar (suffixed '(Discord)' / '(Fluxer)')
- loop protection: bot-authored and webhook-authored messages are ignored
- attachments re-uploaded natively both directions (8 MB cap)
- emoji mirroring: on-demand upload into the receiving guild with LRU
  eviction of bridge-created emojis only; pre-existing emojis untouched;
  to-Discord direction opt-in (50-slot default guild cap)

.env.example

@@ -0,0 +1,9 @@
+DISCORD_TOKEN = ""
+FLUXER_TOKEN = ""
+FLUXER_CLIENT_SECRET = ""
+
+DISCORD_CHANNEL_ID = ""
+FLUXER_CHANNEL_ID = ""
+
+DISCORD_GUILD_ID = ""
+FLUXER_GUILD_ID = ""