Responsive app shell, routes and navigation (#38)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

web/src/shell/Sidebar.module.css

@@ -0,0 +1,78 @@
+.sidebar {
+  width: 208px;
+  padding: 28px 16px;
+  box-sizing: border-box;
+  display: flex;
+  flex-direction: column;
+  background: var(--color-surface);
+}
+
+.wordmark {
+  margin: 0;
+  padding: 0 12px 22px;
+  font-family: var(--font-heading);
+  font-size: 28px;
+  font-weight: 400;
+  color: var(--color-accent);
+}
+
+.nav {
+  display: flex;
+  flex-direction: column;
+  gap: 6px;
+}
+
+.item {
+  display: flex;
+  align-items: center;
+  gap: 12px;
+  min-height: 44px;
+  padding: 12px 16px;
+  box-sizing: border-box;
+  border-radius: var(--radius-pill);
+  color: var(--color-neutral-800);
+  font-size: 15px;
+  font-weight: 700;
+  text-decoration: none;
+}
+
+.active {
+  background: var(--color-accent);
+  color: var(--on-accent);
+}
+
+.household {
+  margin-top: auto;
+  display: flex;
+  align-items: center;
+  gap: 10px;
+  padding: 12px;
+  border-radius: 22px;
+  background: var(--color-bg);
+}
+
+.avatar {
+  width: 36px;
+  height: 36px;
+  flex: none;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  border-radius: 50%;
+  background: var(--color-accent-2-300);
+  color: var(--color-accent-2-900);
+  font-family: var(--font-heading);
+  font-size: 15px;
+}
+
+.householdText {
+  margin: 0;
+  display: flex;
+  flex-direction: column;
+  font-size: 13px;
+  line-height: 1.3;
+}
+
+.householdNote {
+  color: var(--color-neutral-700);
+}