feat: add instance list component and integrate into workspace

- Create InstanceList component with create/start/stop/restart/delete
- Add tool instance icons (external, play, stop)
- Integrate InstanceList into RepoWorkspace sidebar
- Load tool types for instance creation
- Add instance-specific CSS styles

Quality gates: typecheck ✓, lint ✓, build ✓

apps/web/src/styles.css

@@ -2260,3 +2260,64 @@ a.nav-item,
   letter-spacing: 0.05em;
   color: var(--muted);
 }
+
+/* Instance List */
+.instance-list {
+  margin-top: var(--space-4);
+}
+
+.instance-list-header {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  margin-bottom: var(--space-4);
+}
+
+.instance-list-header h3 {
+  margin: 0;
+}
+
+.instance-grid {
+  display: grid;
+  gap: var(--space-3);
+}
+
+.instance-card {
+  display: flex;
+  justify-content: space-between;
+  align-items: center;
+  padding: var(--space-4);
+  background: var(--bg);
+  border: 1px solid var(--border);
+  border-radius: 10px;
+}
+
+.instance-info {
+  display: flex;
+  flex-direction: column;
+  gap: var(--space-1);
+}
+
+.instance-name {
+  font-weight: 600;
+}
+
+.instance-meta {
+  display: flex;
+  align-items: center;
+  gap: var(--space-2);
+  font-size: var(--text-sm);
+  color: var(--muted);
+}
+
+.status-dot {
+  width: 8px;
+  height: 8px;
+  border-radius: 50%;
+}
+
+.instance-actions {
+  display: flex;
+  gap: var(--space-2);
+  align-items: center;
+}