refactor: replace session tabs with sectioned list

src/styles/components.css

@@ -1599,4 +1599,142 @@ button.button-primary {
   @apply flex flex-col h-full;
   background-color: var(--surface-base);
   color: inherit;
+}
+
+/* Session list component */
+.session-list-container {
+  @apply flex flex-col h-full relative;
+  background-color: var(--surface-secondary);
+  min-width: 200px;
+  max-width: 500px;
+}
+
+.session-resize-handle {
+  @apply absolute top-0 right-0 w-1 h-full cursor-col-resize bg-transparent transition-colors;
+  z-index: 10;
+}
+
+.session-resize-handle:hover {
+  background-color: var(--accent-primary);
+}
+
+.session-resize-handle::before {
+  content: "";
+  @apply absolute top-0 left-0 w-2 h-full -translate-x-1/2;
+}
+
+.session-list-header {
+  @apply border-b relative;
+  border-color: var(--border-base);
+}
+
+.session-list-header h3 {
+  color: var(--text-primary);
+  font-size: var(--font-size-sm);
+  font-weight: var(--font-weight-semibold);
+}
+
+.session-header-hints {
+  @apply flex-shrink-0;
+}
+
+.session-list {
+  @apply flex-1;
+}
+
+.session-list-item {
+  @apply border-b last:border-b-0;
+  border-color: var(--border-base);
+}
+
+.session-item-base {
+  @apply w-full flex items-center gap-3 px-3 py-2.5 text-left transition-colors outline-none;
+  font-family: var(--font-family-sans);
+  font-size: var(--font-size-sm);
+}
+
+.session-item-base:focus-visible {
+  @apply ring-2 ring-offset-1;
+  ring-color: var(--accent-primary);
+  ring-offset-color: var(--surface-secondary);
+}
+
+.session-item-active {
+  background-color: var(--accent-primary);
+  color: var(--text-inverted);
+  font-weight: var(--font-weight-medium);
+}
+
+.session-item-inactive {
+  color: var(--text-secondary);
+}
+
+.session-item-inactive:hover {
+  background-color: var(--surface-hover);
+  color: var(--text-primary);
+}
+
+.session-item-special {
+  color: var(--text-muted);
+  font-style: italic;
+}
+
+.session-item-active .session-item-close:hover {
+  background-color: rgba(255, 255, 255, 0.2);
+}
+
+.session-item-title {
+  @apply flex-1 min-w-0;
+  font-weight: inherit;
+}
+
+.session-item-close {
+  @apply flex-shrink-0 p-0.5 rounded transition-all;
+}
+
+.session-item-close:focus-visible {
+  @apply ring-2 ring-offset-1;
+  ring-color: var(--accent-primary);
+  ring-offset-color: inherit;
+}
+
+.session-list-footer {
+  @apply border-t;
+  border-color: var(--border-base);
+}
+
+.session-new-button {
+  background-color: var(--surface-base);
+  color: var(--text-primary);
+  border: 1px solid var(--border-base);
+}
+
+.session-new-button:hover {
+  background-color: var(--surface-hover);
+}
+
+.session-new-button:focus-visible {
+  @apply ring-2 ring-offset-1;
+  ring-color: var(--accent-primary);
+  ring-offset-color: var(--surface-secondary);
+}
+
+[data-theme="dark"] .session-new-button {
+  background-color: var(--surface-base);
+  color: var(--text-primary);
+}
+
+[data-theme="dark"] .session-new-button:hover {
+  background-color: var(--surface-hover);
+}
+
+/* Responsive behavior for session list */
+@media (max-width: 768px) {
+  .session-list-container {
+    min-width: 200px;
+  }
+  
+  .session-item-base {
+    @apply px-2 py-2;
+  }
 }