feat: /ia — chat question-and-answer backed by MiniMax

Adds an `ia` module: `/ia <pergunta>` sends the question to an
OpenAI-compatible chat-completions endpoint (MiniMax by default) and
posts the reply to chat.

Access is gated by `canalhandia.ia`, declared `default: op` so the
operator has it out of the box and LuckPerms can grant it to anyone
else.

The model can only ever produce chat text:

- the reply goes to sendMessage and nowhere else — it is never passed
  to the command dispatcher;
- no `tools`/`tool_choice` are sent, so there is nothing for the model
  to call;
- the system prompt states it has no server, shell or command access;
- replies are sanitised — colour codes stripped so they cannot forge
  server messages, newlines folded so one answer is one chat entry,
  and leading slashes removed so nothing reads as a command to run.

The API key is deliberately not a config value, since config.yml is
committed. It is read from MINIMAX_API_KEY or from
plugins/Canalhandia/minimax.key, which is now gitignored.

Cost is bounded by a per-player cooldown and a server-wide daily cap,
both visible in /canalhandia status. The HTTP call runs off the main
thread; only the delivery hops back onto it.

.gitignore

@@ -1 +1,4 @@
 target/
+
+# The MiniMax API key lives beside the plugin on the server, never in git.
+minimax.key