Add polished answer notifications (#1)

Sends a branded Resend email when a question receives its first answer, records accepted and failed sends, and adds collapsed answer editing with cancel behavior.

Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/store/memory.go

@@ -42,9 +42,17 @@ func (m *Memory) CreateUser(_ context.Context, u *User) error {
 		return fmt.Errorf("invalid role")
 	}
 	u.Username = NormalizeUsername(u.Username)
+	u.Email = NormalizeEmail(u.Email)
 	if _, ok := m.byName[u.Username]; ok {
 		return ErrDuplicateUsername
 	}
+	if u.Email != "" {
+		for _, existing := range m.users {
+			if existing.Email == u.Email {
+				return ErrDuplicateEmail
+			}
+		}
+	}
 	if u.ID == "" {
 		u.ID = uuid.NewString()
 	}
@@ -179,11 +187,21 @@ func (m *Memory) SaveUserProfile(_ context.Context, u *User) error {
 	if !ok {
 		return sql.ErrNoRows
 	}
+	email := NormalizeEmail(u.Email)
+	if email != "" {
+		for id, existing := range m.users {
+			if id != u.ID && existing.Email == email {
+				return ErrDuplicateEmail
+			}
+		}
+	}
 	cur.State = strings.TrimSpace(u.State)
+	cur.Email = email
 	if u.AvatarURL != "" {
 		cur.AvatarURL = u.AvatarURL
 	}
 	u.State = cur.State
+	u.Email = cur.Email
 	u.AvatarURL = cur.AvatarURL
 	return nil
 }