feat(tools): add update-quest tool, switch to Big Pickle (opencode/zen)

- update_quest: aggiorna stato/nome/descrizione missioni
- db: get_quest(), update_quest con nome+desc
- prompt: quest_id nel contesto, esempio nei tool examples
- Switch da deepseek-v4-flash (go) a big-pickle (zen) — gratuito

start.sh

@@ -16,9 +16,9 @@ export DCC_OPENROUTER_KEY="${DCC_OPENROUTER_KEY:-}"
 export DCC_OPENROUTER_MODEL="${DCC_OPENROUTER_MODEL:-openrouter/free}"
 export DCC_OLLAMA_URL="${DCC_OLLAMA_URL:-http://192.168.0.50:11434}"
 export DCC_OLLAMA_MODEL="${DCC_OLLAMA_MODEL:-gemma2:9b}"
-export DCC_LOCAL_URL="${DCC_LOCAL_URL:-https://opencode.ai/zen/go/v1}"
+export DCC_LOCAL_URL="${DCC_LOCAL_URL:-https://opencode.ai/zen/v1}"
 export DCC_LOCAL_KEY="${DCC_LOCAL_KEY:-}"
-export DCC_LOCAL_MODEL="${DCC_LOCAL_MODEL:-deepseek-v4-flash}"
+export DCC_LOCAL_MODEL="${DCC_LOCAL_MODEL:-big-pickle}"
 
 # ── create data dir ────────────────────────────────────────────────
 mkdir -p data