refactor(ui): remaster settings and navigation layout

- Update navigation labels from "My Account" to "Dashboard" and "Login" to "Sign in", updating tests accordingly.
- Redesign settings forms into structured sections with improved spacing and layout.
- Add CSS styles for tabs, small buttons, and responsive settings sections to enhance the user experience.

backend/libs/handlers/accounts_test.go

@@ -387,7 +387,7 @@ func TestAPIDocsHeaderReflectsLoggedInUser(t *testing.T) {
 	}
 	body := response.Body.String()
 	header := body[:strings.Index(body, "<main")]
-	if !strings.Contains(header, "My Account") || strings.Contains(header, ">Login<") || strings.Contains(header, "Health") {
+	if !strings.Contains(header, "Dashboard") || strings.Contains(header, "Sign in") || strings.Contains(header, "Health") {
 		t.Fatalf("api header did not reflect logged-in state: %s", body)
 	}
 }
@@ -404,7 +404,7 @@ func TestAPIDocsHeaderReflectsLoggedOutUser(t *testing.T) {
 	}
 	body := response.Body.String()
 	header := body[:strings.Index(body, "<main")]
-	if !strings.Contains(header, ">Login<") || !strings.Contains(header, ">API<") || strings.Contains(header, "Health") || strings.Contains(header, "My Account") {
+	if !strings.Contains(header, "Sign in") || !strings.Contains(header, ">API<") || strings.Contains(header, "Health") || strings.Contains(header, "Dashboard") {
 		t.Fatalf("api header did not reflect logged-out state: %s", body)
 	}
 }