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/infrastructure/postgres/models/tenant.py

@@ -0,0 +1,27 @@
+import uuid
+from datetime import datetime
+
+from sqlalchemy import CheckConstraint, DateTime, String, func
+from sqlalchemy.dialects.postgresql import JSONB
+from sqlalchemy.orm import Mapped, mapped_column
+
+from src.infrastructure.postgres.models.base import Base
+
+TENANT_STATUSES = ("active", "suspended", "deleted")
+
+
+class Tenant(Base):
+    __tablename__ = "tenants"
+    __table_args__ = (CheckConstraint(f"status IN {TENANT_STATUSES}", name="ck_tenants_status"),)
+
+    id: Mapped[uuid.UUID] = mapped_column(primary_key=True)
+    slug: Mapped[str] = mapped_column(String(80), unique=True, index=True)
+    name: Mapped[str] = mapped_column(String(200))
+    status: Mapped[str] = mapped_column(String(20), default="active", server_default="active")
+    settings: Mapped[dict[str, object]] = mapped_column(JSONB, default=dict, server_default="{}")
+
+    created_at: Mapped[datetime] = mapped_column(DateTime(timezone=True), server_default=func.now())
+    updated_at: Mapped[datetime] = mapped_column(
+        DateTime(timezone=True), server_default=func.now(), onupdate=func.now()
+    )
+    deleted_at: Mapped[datetime | None] = mapped_column(DateTime(timezone=True), default=None)