refactor: move Dashboard to /apps, add Metrics sidebar entry, scope by app

- Route / redirects to /apps, Dashboard serves both /apps and /apps/:id
- When appId is present, exchanges/routes/agents/search are scoped to that app
- Remove Dashboards sidebar link, add Metrics link
- Sidebar section labels (Applications, Agents) are now clickable nav links
  with separate chevron for collapse toggle
- Update all breadcrumbs from Dashboard/href:'/' to Applications/href:'/apps'
- Remove AppDetail page (replaced by scoped Dashboard)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/design-system/layout/Sidebar/Sidebar.module.css

@@ -217,44 +217,6 @@
   gap: 6px;
   width: 100%;
   padding: 8px 12px 4px;
-  font-size: 10px;
-  font-weight: 600;
-  text-transform: uppercase;
-  letter-spacing: 1px;
-  color: var(--sidebar-muted);
-  background: none;
-  border: none;
-  cursor: pointer;
-  text-align: left;
-  transition: color 0.12s;
-}
-
-.treeSectionToggle:hover {
-  color: var(--sidebar-text);
-}
-
-.treeSectionChevron {
-  font-size: 9px;
-  width: 10px;
-  display: inline-flex;
-  align-items: center;
-  justify-content: center;
-}
-
-/* Section header as link (for Agents nav) */
-.treeSectionLink {
-  font-size: 10px;
-  font-weight: 600;
-  text-transform: uppercase;
-  letter-spacing: 1px;
-  color: var(--sidebar-muted);
-  text-decoration: none;
-  flex: 1;
-  transition: color 0.12s;
-}
-
-.treeSectionLink:hover {
-  color: var(--amber-light);
 }
 
 .treeSectionChevronBtn {
@@ -275,6 +237,24 @@
   color: var(--sidebar-text);
 }
 
+.treeSectionLabel {
+  font-size: 10px;
+  font-weight: 600;
+  text-transform: uppercase;
+  letter-spacing: 1px;
+  color: var(--sidebar-muted);
+  cursor: pointer;
+  transition: color 0.12s;
+}
+
+.treeSectionLabel:hover {
+  color: var(--amber-light);
+}
+
+.treeSectionLabelActive {
+  color: var(--amber-light);
+}
+
 .tree {
   list-style: none;
   margin: 0;