feat: AI Dungeon Master engine + web frontend

- Engine: stato SQLite, state machine, 10 approved tools, parser azioni
- LLM: multi-provider (Ollama/OpenRouter/Local), system prompt DCC
- DM cycle: LLM decide tool → engine esegue → narrazione + meccanica
- Dati avventura: JSON machine-readable con 9 aree, mostri, enigmi, quest
- Web: FastAPI + WebSocket backend, SPA frontend dark fantasy
- Ref: architecture-patterns/neon-scratch-lounge (separazione reasoning/execution)

src/engine/providers.py

@@ -0,0 +1,141 @@
+from __future__ import annotations
+
+import json
+import os
+from abc import ABC, abstractmethod
+from typing import Any
+
+import httpx
+
+from src.engine.config import ProviderConfig, load_from_env
+
+
+class LLMProvider(ABC):
+    @abstractmethod
+    def ask(self, prompt: str, system: str = "") -> str:
+        ...
+
+
+class OllamaProvider(LLMProvider):
+    def __init__(self, base_url: str, model: str, timeout: int = 60):
+        self.base_url = base_url.rstrip("/")
+        self.model = model
+        self.timeout = timeout
+
+    def ask(self, prompt: str, system: str = "") -> str:
+        body = {"model": self.model, "prompt": prompt, "stream": False}
+        if system:
+            body["system"] = system
+        resp = httpx.post(
+            f"{self.base_url}/api/generate",
+            json=body,
+            timeout=self.timeout,
+        )
+        resp.raise_for_status()
+        return resp.json().get("response", "")
+
+
+class OpenRouterProvider(LLMProvider):
+    _FREE_FALLBACK = [
+        "openrouter/free",
+        "google/gemma-4-31b-it:free",
+        "qwen/qwen3-coder:free",
+    ]
+
+    def __init__(self, api_key: str, model: str, timeout: int = 60, free_fallback: bool = True):
+        self.api_key = api_key
+        self.model = model
+        self.timeout = timeout
+        self.free_fallback = free_fallback
+
+    def _call(self, model: str, prompt: str, system: str) -> str:
+        messages = []
+        if system:
+            messages.append({"role": "system", "content": system})
+        messages.append({"role": "user", "content": prompt})
+
+        headers = {
+            "Authorization": f"Bearer {self.api_key}",
+            "Content-Type": "application/json",
+        }
+        body = {"model": model, "messages": messages, "stream": False}
+
+        resp = httpx.post(
+            "https://openrouter.ai/api/v1/chat/completions",
+            json=body,
+            headers=headers,
+            timeout=self.timeout,
+        )
+        resp.raise_for_status()
+        return resp.json()["choices"][0]["message"]["content"]
+
+    def ask(self, prompt: str, system: str = "") -> str:
+        models = [self.model]
+        if self.free_fallback:
+            models.extend(self._FREE_FALLBACK)
+        last_err = None
+        for m in models:
+            try:
+                return self._call(m, prompt, system)
+            except Exception as e:
+                last_err = e
+                continue
+        raise last_err  # type: ignore
+
+
+class LocalProvider(LLMProvider):
+    def __init__(self, base_url: str, model: str, api_key: str = "", timeout: int = 60):
+        self.base_url = base_url.rstrip("/")
+        self.model = model
+        self.api_key = api_key
+        self.timeout = timeout
+
+    def ask(self, prompt: str, system: str = "") -> str:
+        messages = []
+        if system:
+            messages.append({"role": "system", "content": system})
+        messages.append({"role": "user", "content": prompt})
+
+        headers = {"Content-Type": "application/json"}
+        if self.api_key:
+            headers["Authorization"] = f"Bearer {self.api_key}"
+
+        body = {"model": self.model, "messages": messages, "stream": False}
+
+        resp = httpx.post(
+            f"{self.base_url}/chat/completions",
+            json=body,
+            headers=headers,
+            timeout=self.timeout,
+        )
+        resp.raise_for_status()
+        data = resp.json()
+        return data["choices"][0]["message"]["content"]
+
+
+_registry: dict[str, Any] = {
+    "ollama": OllamaProvider,
+    "openrouter": OpenRouterProvider,
+    "local": LocalProvider,
+}
+
+
+def create_provider(cfg: ProviderConfig | None = None) -> LLMProvider:
+    if cfg is None:
+        cfg = load_from_env()
+
+    cls = _registry.get(cfg.kind)
+    if not cls:
+        raise ValueError(f"Provider sconosciuto: {cfg.kind} (disponibili: {list(_registry.keys())})")
+
+    if cfg.kind == "ollama":
+        return cls(cfg.ollama_base_url, cfg.ollama_model, cfg.timeout)
+    elif cfg.kind == "openrouter":
+        key = cfg.openrouter_api_key or os.getenv("OPENROUTER_API_KEY", "")
+        if not key:
+            raise ValueError("OPENROUTER_API_KEY non configurata")
+        return cls(key, cfg.openrouter_model, cfg.timeout, cfg.openrouter_free_fallback)
+    elif cfg.kind == "local":
+        return cls(cfg.local_base_url, cfg.local_model, cfg.local_api_key, cfg.timeout)
+    else:
+        raise ValueError(f"Provider non implementato: {cfg.kind}")