Add FastAPI backend with agent system

backend/app/config.py

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+from pydantic_settings import BaseSettings, SettingsConfigDict
+from typing import Literal
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8", extra="ignore")
+
+    # === 应用基础 ===
+    APP_NAME: str = "Jarvis"
+    APP_VERSION: str = "0.1.0"
+    DEBUG: bool = False
+
+    # === 安全 ===
+    SECRET_KEY: str = "change-me-in-production"
+    ALGORITHM: str = "HS256"
+    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 7
+
+    # === 数据库 ===
+    DATABASE_URL: str = "sqlite+aiosqlite:///./data/jarvis.db"
+    DATA_DIR: str = "./data"
+
+    # === ChromaDB ===
+    CHROMA_PERSIST_DIR: str = "./data/chroma"
+
+    # === LLM 配置 ===
+    # 支持: openai / claude / ollama / deepseek / custom
+    LLM_PROVIDER: Literal["openai", "claude", "ollama", "deepseek", "custom"] = "openai"
+
+    # OpenAI (默认)
+    OPENAI_API_KEY: str = ""
+    OPENAI_MODEL: str = "gpt-4o"
+    OPENAI_BASE_URL: str = "https://api.openai.com/v1"
+
+    # Claude
+    ANTHROPIC_API_KEY: str = ""
+    CLAUDE_MODEL: str = "claude-sonnet-4-20250514"
+    CLAUDE_MAX_TOKENS: int = 8192
+
+    # Ollama (本地模型)
+    OLLAMA_BASE_URL: str = "http://localhost:11434"
+    OLLAMA_MODEL: str = "llama3"
+
+    # === 定时任务 ===
+    SCHEDULER_ENABLED: bool = True
+    DAILY_PLAN_TIME: str = "00:00"
+    FORUM_SCAN_INTERVAL_MINUTES: int = 30
+
+    # === CORS ===
+    CORS_ORIGINS: list[str] = ["http://localhost:5173", "http://localhost:3000"]
+
+    # === 文件上传 ===
+    UPLOAD_DIR: str = "./data/uploads"
+    MAX_UPLOAD_SIZE: int = 50 * 1024 * 1024
+
+    # === 向量化 ===
+    EMBEDDING_MODEL: str = "text-embedding-3-small"
+    CHUNK_SIZE: int = 500
+    CHUNK_OVERLAP: int = 50
+
+    # === LangSmith 可观测性 ===
+    LANGSMITH_TRACING: bool = False
+    LANGSMITH_API_KEY: str = ""
+    LANGSMITH_PROJECT: str = "jarvis-agent"
+
+    # === NAS 部署 ===
+    NAS_DATA_ROOT: str = "/data/jarvis"
+
+
+settings = Settings()