feat: Settings page, DELETE traces endpoint, Anthropic SDK, dashboard bug fixes

- Add /dashboard/settings with SDK connection details, data stats, purge
- Add DELETE /api/traces/[id] with cascade deletion
- Add Anthropic integration (wrap_anthropic) for Python SDK
- Fix missing root duration (totalDuration -> durationMs mapping)
- Fix truncated JSON in decision tree nodes (extract readable labels)
- Fix hardcoded 128K maxTokens in token gauge (model-aware context windows)
- Enable Settings nav item in sidebar

apps/web/src/app/dashboard/layout.tsx

@@ -22,7 +22,7 @@ interface NavItem {
 const navItems: NavItem[] = [
   { href: "/dashboard", label: "Traces", icon: Activity },
   { href: "/dashboard/decisions", label: "Decisions", icon: GitBranch },
-  { href: "/dashboard/settings", label: "Settings", icon: Settings, comingSoon: true },
+  { href: "/dashboard/settings", label: "Settings", icon: Settings },
 ];
 
 function Sidebar({ onNavigate }: { onNavigate?: () => void }) {