Convert the following Python FastAPI project to Go using Chi router and modernc.org/sqlite.

OUTPUT: Return ALL files with === markers:
=== go.mod ===
=== models.go ===
=== handlers.go ===
=== main.go ===
=== handlers_test.go ===

CONVERSION RULES:
- package main for all files
- Pydantic models → Go structs with json tags
- SQLAlchemy ORM → database/sql with raw SQL and RETURNING clause
- FastAPI routes → Chi router: r.Post("/path", handler(db))
- Handlers are closures: func handler(db *sql.DB) http.HandlerFunc
- Depends(get_db) → State passed via closure over *sql.DB
- HTTPException(404) → http.Error(w, "not found", http.StatusNotFound)
- POST returns http.StatusCreated (201), DELETE returns http.StatusNoContent (204)
- sql.ErrNoRows for not-found checks
- TestClient → httptest.NewServer + setupTestServer helper
- test.db → sql.Open("sqlite", ":memory:")
- Empty list: return []Entity{} not nil
- import _ "modernc.org/sqlite" (pure Go driver, no CGO)
- import "github.com/go-chi/chi/v5"
- No markdown fences in output — just raw code