feat: protect write endpoints with JWT auth (story #08)

Add bcrypt user file auth, JWT middleware on all write routes, Pinia
authStore with localStorage persistence, login view with redirect
support, and v-if guards on all CRUD controls and admin nav link.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/internal/handler/auth_handler_test.go

@@ -0,0 +1,75 @@
+package handler_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"golang.org/x/crypto/bcrypt"
+
+	"github.com/labstack/echo/v4"
+
+	"osdb/internal/handler"
+)
+
+func makeUsersMap(username, password string) map[string]string {
+	h, _ := bcrypt.GenerateFromPassword([]byte(username+":"+password), bcrypt.MinCost)
+	return map[string]string{username: string(h)}
+}
+
+func TestAuthHandler_Login_ValidCredentials(t *testing.T) {
+	users := makeUsersMap("admin", "secret")
+	h := handler.NewAuthHandler(users, "jwttest")
+
+	body := `{"username":"admin","password":"secret"}`
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/auth/login", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+	c := echo.New().NewContext(req, rec)
+
+	if err := h.Login(c); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rec.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d — body: %s", rec.Code, rec.Body.String())
+	}
+	if !strings.Contains(rec.Body.String(), "token") {
+		t.Errorf("expected 'token' in response, got: %s", rec.Body.String())
+	}
+}
+
+func TestAuthHandler_Login_InvalidCredentials(t *testing.T) {
+	users := makeUsersMap("admin", "secret")
+	h := handler.NewAuthHandler(users, "jwttest")
+
+	body := `{"username":"admin","password":"wrong"}`
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/auth/login", strings.NewReader(body))
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+	c := echo.New().NewContext(req, rec)
+
+	if err := h.Login(c); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rec.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", rec.Code)
+	}
+}
+
+func TestAuthHandler_Login_MissingBody(t *testing.T) {
+	users := makeUsersMap("admin", "secret")
+	h := handler.NewAuthHandler(users, "jwttest")
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/auth/login", nil)
+	req.Header.Set("Content-Type", "application/json")
+	rec := httptest.NewRecorder()
+	c := echo.New().NewContext(req, rec)
+
+	if err := h.Login(c); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if rec.Code != http.StatusUnauthorized {
+		t.Errorf("expected 401, got %d", rec.Code)
+	}
+}