feat(bootstrap,api,infra): scaffold app composition, health route, and postgres/minio/qdrant adapters

Why:
- first runnable slice of ADR-0012's resource-lifetime rules and ADR-0015's package layout: app-lifetime clients built once in the lifespan, released via explicit dependencies.

Changes:
- Settings split into per-domain nested settings (postgres/minio/ingestion/qdrant/app/logging); FastAPI app wired with /healthz, /readyz and a /v1 router; Postgres/MinIO/Qdrant adapters and SQLAlchemy models for tenants, API keys, source files, ingestion jobs/events.

src/config.py

@@ -1,5 +1,76 @@
-from pydantic_settings import BaseSettings
+from pydantic import Field
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class PostgresSettings(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="POSTGRES_", extra="ignore")
+
+    host: str = "127.0.0.1"
+    port: int = 5433
+    user: str = "chatbot"
+    password: str = "chatbot"
+    db: str = "chatbot"
+
+    @property
+    def dsn(self) -> str:
+        return f"postgresql+asyncpg://{self.user}:{self.password}@{self.host}:{self.port}/{self.db}"
+
+
+class MinioSettings(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="MINIO_", extra="ignore")
+
+    endpoint: str = "127.0.0.1:9100"
+    access_key: str = "chatbot"
+    secret_key: str = "chatbot-secret"
+    secure: bool = False
+    bucket: str = "chatbot-source-files"
+
+
+class IngestionSettings(BaseSettings):
+    """Bounds on inline ingestion (ADR-0017).
+
+    `timeout_seconds` must stay below the proxy/load-balancer/client read
+    timeouts, or callers give up on work that is still succeeding.
+    """
+
+    model_config = SettingsConfigDict(env_prefix="INGESTION_", extra="ignore")
+
+    max_concurrency: int = 4
+    thread_pool_size: int = 8
+    timeout_seconds: float = 120.0
+    max_chunks_per_file: int = 5000
+    embed_batch_size: int = 128
+    embed_concurrency: int = 4
+
+
+class QdrantSettings(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="QDRANT_", extra="ignore")
+
+    url: str = "http://127.0.0.1:6343"
+    api_key: str | None = None
+
+
+class AppLimitSettings(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="APP_", extra="ignore")
+
+    env: str = "local"
+    max_upload_size_mb: int = 25
+    readiness_check_timeout_seconds: float = 2.0
+
+
+class LoggingSettings(BaseSettings):
+    model_config = SettingsConfigDict(env_prefix="LOG_", extra="ignore")
+
+    level: str = "INFO"
+    json_format: bool = False
 
 
 class Settings(BaseSettings):
-    pass
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    postgres: PostgresSettings = Field(default_factory=PostgresSettings)
+    minio: MinioSettings = Field(default_factory=MinioSettings)
+    ingestion: IngestionSettings = Field(default_factory=IngestionSettings)
+    qdrant: QdrantSettings = Field(default_factory=QdrantSettings)
+    app: AppLimitSettings = Field(default_factory=AppLimitSettings)
+    logging: LoggingSettings = Field(default_factory=LoggingSettings)