Redesign backend layout: dark sidebar + slim topbar

Moves from a floating-card sidebar to a full-height dark sidebar
(bg-neutral) with the club logo at the top and logged-in user pinned
to the bottom. The topbar becomes a slim bar containing only the
mobile hamburger, notifications, and logout — no duplicate logo.

- base.html: DaisyUI drawer with h-screen/overflow-hidden so the
  sidebar is sticky and the content column scrolls independently.
  The #content div is now the white card (bg-base-100 rounded-xl)
  so HTMX innerHTML swaps stay inside it.
- member_filter.html: replaces the .action_bar component with a
  clean flex row (title + Add button) above a plain filter form.
  Table and mobile card list are unchanged.
- styles.css: adds .sidebar-nav scoped overrides for menu link
  hover/active colours on the dark sidebar; reduces h1.page-title
  bottom margin from mb-12 to mb-4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

theme/static_src/src/styles.css

@@ -62,7 +62,7 @@
 @layer components {
     h1.page-title {
         @apply text-3xl font-bold;
-        @apply mb-12;
+        @apply mb-4;
 
         & > svg {
             @apply mr-2;
@@ -104,6 +104,39 @@
             @apply min-w-fit lg:w-fit;
         }
     }
+
+    /*
+     * Sidebar navigation — dark background overrides.
+     * .sidebar-nav wraps the <ul class="menu"> inside the dark aside, so these
+     * rules only apply there and leave DaisyUI's default menu colours intact
+     * everywhere else (e.g. inside modals or dropdowns).
+     */
+    .sidebar-nav .menu .menu-title {
+        color: color-mix(in oklab, var(--color-neutral-content) 40%, transparent);
+        font-size: 0.7rem;
+        text-transform: uppercase;
+        letter-spacing: 0.1em;
+        padding-inline: 0.75rem;
+    }
+
+    /* Default nav link on dark sidebar */
+    .sidebar-nav .menu li > a {
+        color: color-mix(in oklab, var(--color-neutral-content) 70%, transparent);
+        border-radius: var(--radius-box);
+        transition: background-color 0.15s, color 0.15s;
+    }
+
+    /* Hover state */
+    .sidebar-nav .menu li > a:hover {
+        background-color: color-mix(in oklab, white 10%, transparent);
+        color: var(--color-neutral-content);
+    }
+
+    /* Active state (set by template class or JS menuHighlight event) */
+    .sidebar-nav .menu li > a.menu-active {
+        background-color: color-mix(in oklab, var(--color-primary) 85%, transparent);
+        color: var(--color-primary-content);
+    }
 }
 
 .choices {