feat(core): add core layer with config, clients, exceptions, models, and app factory

src/core/config.py

@@ -0,0 +1,39 @@
+"""Application configuration loaded from .env via pydantic-settings."""
+
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    """All environment variables with defaults and validation."""
+
+    model_config = SettingsConfigDict(env_file=".env", env_file_encoding="utf-8")
+
+    # OpenAI
+    openai_api_key: str
+    embedding_model: str = "text-embedding-3-small"
+    llm_model: str = "gpt-4o-mini"
+
+    # Qdrant
+    qdrant_url: str = "http://localhost:6333"
+    qdrant_api_key: str | None = None
+
+    # Retrieval
+    top_k: int = 5
+
+    # LLM generation
+    temperature: float = 0.0
+    max_tokens: int = 1024
+
+    # Chunking defaults
+    chunk_size: int = 512
+    chunk_overlap: int = 50
+
+    # Semantic chunking
+    semantic_threshold: float = 0.3
+    semantic_min_chunk_size: int = 3
+
+    # Database
+    database_url: str = "sqlite:///./data/chunking_benchmark.db"
+
+
+settings = Settings()