feat: enhance CI workflow and update webapp styles

- Added Node.js setup and webapp testing steps to the CI workflow for improved integration.
- Updated HTML to link multiple CSS files for better modularity and organization of styles.
- Removed deprecated `style.css` and introduced new CSS files for base styles, calendar, day detail, hints, markers, states, and duty list to enhance maintainability and readability.
- Implemented new styles for improved presentation of duty information and user interactions.
- Added unit tests for new API functions and contact link rendering to ensure functionality and reliability.

webapp/js/api.js

@@ -67,31 +67,26 @@ export async function apiGet(path, params = {}, options = {}) {
  * @returns {Promise<object[]>}
  */
 export async function fetchDuties(from, to, signal) {
-  try {
-    const res = await apiGet("/api/duties", { from, to }, { signal });
-    if (res.status === 403) {
-      let detail = t(state.lang, "access_denied");
-      try {
-        const body = await res.json();
-        if (body && body.detail !== undefined) {
-          detail =
-            typeof body.detail === "string"
-              ? body.detail
-              : (body.detail.msg || JSON.stringify(body.detail));
-        }
-      } catch (parseErr) {
-        /* ignore */
+  const res = await apiGet("/api/duties", { from, to }, { signal });
+  if (res.status === 403) {
+    let detail = t(state.lang, "access_denied");
+    try {
+      const body = await res.json();
+      if (body && body.detail !== undefined) {
+        detail =
+          typeof body.detail === "string"
+            ? body.detail
+            : (body.detail.msg || JSON.stringify(body.detail));
       }
-      const err = new Error("ACCESS_DENIED");
-      err.serverDetail = detail;
-      throw err;
+    } catch (parseErr) {
+      /* ignore */
     }
-    if (!res.ok) throw new Error(t(state.lang, "error_load_failed"));
-    return res.json();
-  } catch (e) {
-    if (e.name === "AbortError") throw e;
-    throw e;
+    const err = new Error("ACCESS_DENIED");
+    err.serverDetail = detail;
+    throw err;
   }
+  if (!res.ok) throw new Error(t(state.lang, "error_load_failed"));
+  return res.json();
 }
 
 /**