💄 style(css): remove light mode overrides

- delete CSS rules for light mode to maintain a single dark mode theme

♻️ refactor(html): enforce dark mode and remove theme toggle

- simplify theme management by permanently enabling dark mode
- remove theme toggle button and related JavaScript logic

app/templates/base.html

@@ -22,16 +22,8 @@
     <link rel="stylesheet" href="/static/style.css" />
 
     <script>
-      // Apply persisted theme preference; default is dark.
-      (function () {
-        const stored = localStorage.getItem("fleetledger-theme");
-        const html = document.getElementById("html-root");
-        if (stored === "light") {
-          html.classList.remove("dark");
-        } else {
-          html.classList.add("dark");
-        }
-      })();
+      // Always force dark mode (no toggle).
+      document.documentElement.classList.add("dark");
     </script>
 
     {% block extra_head %}{% endblock %}
@@ -103,13 +95,6 @@
                 {% if not loop.last %}<span class="text-slate-700">|</span>{% endif %}
               {% endfor %}
             </div>
-            <button
-              id="theme-toggle"
-              class="rounded-lg border border-slate-700 bg-slate-900/60 px-2.5 py-1 text-slate-300 hover:border-slate-500 hover:text-white"
-              type="button"
-            >
-              🌓
-            </button>
           </div>
         </div>
       </header>
@@ -129,13 +114,6 @@
     </div>
 
     <script>
-      // Theme toggle button handler
-      document.getElementById("theme-toggle").addEventListener("click", () => {
-        const html = document.getElementById("html-root");
-        const isDark = html.classList.toggle("dark");
-        localStorage.setItem("fleetledger-theme", isDark ? "dark" : "light");
-      });
-
       // Register service worker for PWA
       if ("serviceWorker" in navigator) {
         navigator.serviceWorker