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)

README.md

@@ -1,3 +1,34 @@
 # itako
 
-discord.gg <---> fluxer.app channel bridge. unifies platforms, unifies friends.
+discord.gg <---> fluxer.app channel bridge. unifies platforms, unifies friends.
+
+One channel on each side; messages are relayed through webhooks so they show
+the original author's name and avatar.
+
+## Docs
+
+- **[INSTALL.md](INSTALL.md)** — setup guide (bots, tokens, .env, running)
+- **[TODO.md](TODO.md)** — roadmap: edit/delete sync, stickers, service mode, …
+
+## Layout
+
+- `itako/bridge.py` — runs both bots in one asyncio process:
+  - discord.py bot listens on Discord, relays to a **Fluxer** webhook
+  - fluxer.py `Bot` listens on Fluxer, relays to a **Discord** webhook
+- Webhooks named `itako-bridge` (configurable) are created once per channel
+  and reused.
+
+## Setup
+
+1. `uv sync`
+2. Copy `.env.example` to `.env` and fill in (see [INSTALL.md](INSTALL.md)):
+   - Discord: bot token + the channel ID to bridge (enable Message Content intent!)
+   - Fluxer: create a bot application at fluxer.app, grab its token, invite it
+     to your guild, put its token + the channel ID
+3. `uv run python -m itako.bridge`
+
+## Loop protection
+
+- Messages authored by either bot account are ignored.
+- Messages posted by either side's webhook (`message.webhook_id`) are ignored,
+  so relayed copies never bounce back.