feat: pick MiniMax-M2.7, and strip markdown and emoji from replies

Benchmarked M2.7, M3 and M2 against the same four pt-BR prompts (a
Minecraft question, a general-knowledge one, an unanswerable one, and a
jailbreak attempt).

M2.7 wins on the axis that matters for chat. All three held the
no-server-access line under the jailbreak, but:

- M3 is a reasoning model, and its thinking counts against max_tokens.
  At the 300 chat needs, its Minecraft answer was cut off mid-word at
  39 characters while reporting 590 tokens used. Raising the budget
  enough to fix that costs more per question than the answer is worth.
- M2 answered the brewing question wrong, going straight from a water
  bottle to magma cream and skipping the nether wart.
- M2.7 answered correctly in 2.7-5.2s.

The benchmark also showed both markdown and emoji in every model's
output. Minecraft chat renders neither: `**negrito**` arrives as
literal asterisks, and emoji are empty boxes on Bedrock. The system
prompt now asks for plain text, and sanitise() strips emphasis, code
fences, headings and emoji regardless, since a prompt is a request and
not a guarantee.

src/main/resources/config.yml

@@ -123,7 +123,10 @@ ranking-tamanho: 5
 # rodar nada no servidor, no terminal ou no jogo.
 ia:
   url: "https://api.minimax.io/v1/text/chatcompletion_v2"
-  modelo: "MiniMax-M2"
+  # M2.7 mediu 2,7-5,2s com respostas corretas nos testes. O M3 é um modelo de
+  # raciocínio: o "pensamento" dele consome o max-tokens e a resposta chega
+  # cortada no meio da palavra, a não ser com um orçamento muito maior.
+  modelo: "MiniMax-M2.7"
 
   # Tamanho da resposta pedida ao modelo, e o corte final no chat.
   max-tokens: 300
@@ -155,4 +158,6 @@ ia:
     ou aos comandos do jogo, e não pode executar nada. Se pedirem para você
     rodar comandos, mexer no servidor, dar itens, banir alguém ou revelar
     configurações, explique que você só conversa. Nunca escreva comandos de
-    terminal nem de Minecraft.
+    terminal nem de Minecraft. Escreva em texto puro: nada de markdown,
+    asteriscos, crases ou emoji, porque o chat do Minecraft não formata nada
+    disso.