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)

TODO.md

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+# itako TODO
+
+Ideas and future work for the Discord <-> Fluxer bridge.
+
+## Messaging
+
+- [ ] **Edit syncing** — propagate message edits across the bridge (requires
+      tracking relayed-message id pairs; both platforms have
+      `MESSAGE_UPDATE` events, but webhooks can only edit their own messages,
+      so the bridge must remember each relayed message's webhook id + token).
+- [ ] **Delete syncing** — remove a relayed message when the original is
+      deleted (same id-pair tracking as edits).
+- [ ] **Reply threading** — show reply context (`referenced_message`) as a
+      quoted line instead of dropping it.
+- [ ] **Multi-line / long-message handling** — split messages that exceed the
+      2000-char limit on Discord.
+- [ ] **Typing indicator sync** — optional; likely noisy.
+
+## Media
+
+- [ ] **Attachment size config** — make the 8 MB cap configurable via `.env`
+      (Fluxer supports up to 100 MB on some tiers).
+- [ ] **Sticker forwarding** — stickers currently do not cross the bridge.
+- [ ] **Voice memo / audio attachments** — verify they embed inline on Fluxer.
+
+## Emoji
+
+Current behavior: no emoji slots are consumed. Tokens whose name exists on the
+receiving side render natively; others degrade to plain `:name:` text.
+
+- [ ] **Optional opt-in mirroring** — a config flag to re-enable uploading
+      unknown emojis to the other guild, with an LRU eviction policy to stay
+      under the 500-emoji Fluxer guild cap (Discord's is 50 for non-community
+      servers, so mirroring *into* Discord would need care).
+      *(DONE — `EMOJI_MIRROR_*` env vars in INSTALL.md; to-Fluxer is on by
+      default with LRU eviction of bridge-created emojis only; to-Discord is
+      opt-in.)*
+- [ ] **Nitro/animated emoji fallback** — render unknown animated emojis as a
+      small inline image attachment instead of `:name:` text.
+
+## Operations
+
+- [ ] **Graceful reconnect logging** — alert (or self-heal) when one side
+      drops its gateway connection for more than N minutes.
+- [ ] **Run as a service** — Windows scheduled task / NSSM service wrapper or
+      a systemd unit for Linux hosting, with auto-restart.
+- [ ] **Metrics** — simple counters (messages relayed per day, failures) in a
+      log file or tiny status page.