Feat: Build out server shell

Frontend/src/components/shell/TopBar/ThemeToggle.module.scss

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+.toggleButton {
+  display: inline-flex;
+  justify-content: center;
+  align-items: center;
+  width: 2.75rem;
+  height: 2.75rem;
+  aspect-ratio: 1;
+  padding: 0;
+  border: 0;
+  border-radius: 999px;
+  flex-shrink: 0;
+  cursor: pointer;
+  background: transparent;
+  color: var(--color-text-muted);
+  transition:
+    background-color 500ms ease,
+    color 220ms var(--easing-standard),
+    transform 180ms var(--easing-standard);
+}
+
+.toggleButton:hover {
+  background: color-mix(in srgb, var(--color-text) 8%, transparent);
+  color: var(--color-text);
+}
+
+.toggleButton:focus-visible {
+  outline: none;
+  background: color-mix(in srgb, var(--color-accent-strong) 12%, transparent);
+  box-shadow: 0 0 0 0.12rem color-mix(in srgb, var(--color-accent-strong) 28%, transparent);
+  color: var(--color-text);
+}
+
+.iconContainer {
+  position: relative;
+  width: 1.375rem;
+  height: 1.375rem;
+}
+
+.iconLayer {
+  position: absolute;
+  inset: 0;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  transition:
+    transform 1000ms ease,
+    opacity 500ms ease;
+}
+
+.moonLayer {
+  transform: rotate(90deg);
+  opacity: 0;
+
+  :global([data-theme="dark"]) & {
+    transform: rotate(0deg);
+    opacity: 1;
+  }
+}
+
+.sunLayer {
+  transform: rotate(0deg);
+  opacity: 1;
+
+  :global([data-theme="dark"]) & {
+    transform: rotate(-90deg);
+    opacity: 0;
+  }
+}