feat(llm): провайдер за протоколом — OpenAI-совместимый API и mock, фабрика по конфигу

- LLMProvider: complete(messages, schema) -> LLMResult (текст, разобранный JSON, токены)
- openai_compat: /chat/completions, structured output через response_format json_schema,
  JSON из ```-обёртки тоже разбирается; ретраи на 429/5xx и сетевые ошибки, 4xx — сразу ошибка
- mock: детерминированные правила для тестов и демо без сети
- LLMSettings (LLM_PROVIDER/BASE_URL/MODEL/API_KEY…), CLI python -m app.llm.cli

Refs #17

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/config.py

@@ -1,7 +1,7 @@
 """Typed configuration from the environment / `.env` — one settings class per subsystem (ARCHITECTURE §2.11)."""
 
 from pathlib import Path
-from typing import Annotated
+from typing import Annotated, Literal
 
 from pydantic import Field, SecretStr, field_validator
 from pydantic_settings import BaseSettings, NoDecode, SettingsConfigDict
@@ -29,6 +29,19 @@ class AccessSettings(BaseSettings):
         return value
 
 
+class LLMSettings(BaseSettings):
+    model_config = SettingsConfigDict(**_ENV, env_prefix="LLM_")
+
+    # mock: deterministic offline answers (tests, demo without network); openai_compat: any OpenAI-style API (ADR-008)
+    provider: Literal["mock", "openai_compat"] = "mock"
+    base_url: str = ""
+    model: str = ""
+    api_key: SecretStr = SecretStr("")
+    timeout: float = Field(default=30.0, gt=0)
+    max_attempts: int = Field(default=3, ge=1)
+    temperature: float = Field(default=0.0, ge=0, le=2)
+
+
 class RuntimeSettings(BaseSettings):
     model_config = _ENV
 
@@ -46,4 +59,5 @@ class Settings(BaseSettings):
 
     telegram: TelegramSettings = Field(default_factory=TelegramSettings)
     access: AccessSettings = Field(default_factory=AccessSettings)
+    llm: LLMSettings = Field(default_factory=LLMSettings)
     runtime: RuntimeSettings = Field(default_factory=RuntimeSettings)