feat: enhance UI components and error handling

- Updated HTML structure for navigation buttons in the calendar, adding SVG icons for improved visual clarity.
- Introduced a new muted text style in CSS for better presentation of empty duty list messages.
- Enhanced calendar CSS for navigation buttons and day indicators, improving layout and responsiveness.
- Improved error handling in the UI by adding retry functionality to the error display, allowing users to retry actions directly from the error message.
- Updated internationalization messages to include a retry option for error handling.
- Added unit tests to verify the new error handling behavior and UI updates.

webapp/css/states.css

@@ -33,7 +33,7 @@
   }
 }
 
-.loading, .error {
+.loading {
   text-align: center;
   padding: 12px;
   color: var(--muted);
@@ -45,7 +45,16 @@
 }
 
 .error {
+  display: flex;
+  flex-direction: column;
+  align-items: center;
+  gap: 12px;
+  padding: 20px 16px;
+  margin: 12px 0;
+  background: var(--surface);
+  border-radius: 12px;
   color: var(--error);
+  text-align: center;
 }
 
 .error[hidden], .loading.hidden,
@@ -53,6 +62,36 @@
   display: none !important;
 }
 
+.error-icon {
+  flex-shrink: 0;
+  color: var(--error);
+}
+
+.error-text {
+  margin: 0;
+}
+
+.error-retry {
+  margin-top: 4px;
+  padding: 8px 16px;
+  font-size: 0.9rem;
+  font-weight: 500;
+  color: var(--bg);
+  background: var(--accent);
+  border: none;
+  border-radius: 8px;
+  cursor: pointer;
+}
+
+.error-retry:hover {
+  opacity: 0.9;
+}
+
+.error-retry:focus-visible {
+  outline: 2px solid var(--accent);
+  outline-offset: 2px;
+}
+
 /* Current duty view (Mini App deep link startapp=duty) */
 [data-view="currentDuty"] .calendar-sticky,
 [data-view="currentDuty"] .duty-list {
@@ -167,11 +206,19 @@
   color: var(--muted);
   margin-bottom: 16px;
   line-height: 0;
+  width: 48px;
+  height: 48px;
+  border-radius: 50%;
+  background: color-mix(in srgb, var(--muted) 25%, transparent);
+  padding: 12px;
+  box-sizing: border-box;
 }
 
 .current-duty-no-duty-icon svg {
   display: block;
-  opacity: 0.7;
+  width: 100%;
+  height: 100%;
+  opacity: 0.85;
 }
 
 .current-duty-no-duty {
@@ -282,8 +329,12 @@
 
 .access-denied {
   text-align: center;
-  padding: 24px 12px;
+  padding: 24px 16px;
+  margin: 12px 0;
+  background: var(--surface);
+  border-radius: 12px;
   color: var(--muted);
+  box-shadow: 0 1px 3px color-mix(in srgb, var(--text) 8%, transparent);
 }
 
 .access-denied p {