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/auth/auth_test.go

@@ -0,0 +1,125 @@
+package auth_test
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+
+	"golang.org/x/crypto/bcrypt"
+
+	"osdb/internal/auth"
+)
+
+// hashPepper mirrors the pepper convention: bcrypt("username:password")
+func hashPepper(username, password string) string {
+	h, err := bcrypt.GenerateFromPassword([]byte(username+":"+password), bcrypt.MinCost)
+	if err != nil {
+		panic(err)
+	}
+	return string(h)
+}
+
+func writeTempUsersFile(t *testing.T, content string) string {
+	t.Helper()
+	f, err := os.CreateTemp(t.TempDir(), "users*.env")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.WriteString(content); err != nil {
+		t.Fatal(err)
+	}
+	f.Close()
+	return f.Name()
+}
+
+func TestLoadUsers_ParsesValidFile(t *testing.T) {
+	hash := hashPepper("admin", "secret")
+	path := writeTempUsersFile(t, "admin:"+hash+"\n")
+
+	users, err := auth.LoadUsers(path)
+	if err != nil {
+		t.Fatalf("LoadUsers: %v", err)
+	}
+	if len(users) != 1 {
+		t.Fatalf("expected 1 user, got %d", len(users))
+	}
+	if _, ok := users["admin"]; !ok {
+		t.Error("expected 'admin' in users map")
+	}
+}
+
+func TestLoadUsers_SkipsCommentLines(t *testing.T) {
+	hash := hashPepper("admin", "secret")
+	content := "# comment\nadmin:" + hash + "\n"
+	path := writeTempUsersFile(t, content)
+
+	users, err := auth.LoadUsers(path)
+	if err != nil {
+		t.Fatalf("LoadUsers: %v", err)
+	}
+	if len(users) != 1 {
+		t.Fatalf("expected 1 user, got %d", len(users))
+	}
+}
+
+func TestLoadUsers_MissingFile(t *testing.T) {
+	_, err := auth.LoadUsers(filepath.Join(t.TempDir(), "nonexistent.env"))
+	if err == nil {
+		t.Error("expected error for missing file")
+	}
+}
+
+func TestVerifyPassword_CorrectPassword(t *testing.T) {
+	hash := hashPepper("admin", "secret")
+	users := map[string]string{"admin": hash}
+
+	if !auth.VerifyPassword(users, "admin", "secret") {
+		t.Error("expected password to match")
+	}
+}
+
+func TestVerifyPassword_WrongPassword(t *testing.T) {
+	hash := hashPepper("admin", "secret")
+	users := map[string]string{"admin": hash}
+
+	if auth.VerifyPassword(users, "admin", "wrong") {
+		t.Error("expected password to not match")
+	}
+}
+
+func TestVerifyPassword_UnknownUser(t *testing.T) {
+	if auth.VerifyPassword(map[string]string{}, "nobody", "secret") {
+		t.Error("expected false for unknown user")
+	}
+}
+
+func TestGenerateAndValidateJWT(t *testing.T) {
+	token, err := auth.GenerateJWT("admin", "testsecret")
+	if err != nil {
+		t.Fatalf("GenerateJWT: %v", err)
+	}
+	if token == "" {
+		t.Error("expected non-empty token")
+	}
+
+	claims, err := auth.ValidateJWT(token, "testsecret")
+	if err != nil {
+		t.Fatalf("ValidateJWT: %v", err)
+	}
+	if claims.Username != "admin" {
+		t.Errorf("expected username 'admin', got %q", claims.Username)
+	}
+}
+
+func TestValidateJWT_WrongSecret(t *testing.T) {
+	token, _ := auth.GenerateJWT("admin", "correct")
+	if _, err := auth.ValidateJWT(token, "wrong"); err == nil {
+		t.Error("expected error for wrong secret")
+	}
+}
+
+func TestValidateJWT_MalformedToken(t *testing.T) {
+	if _, err := auth.ValidateJWT("not.a.token", "secret"); err == nil {
+		t.Error("expected error for malformed token")
+	}
+}