feat: add procedural flows with intake forms, navigation, and seed templates

Adds a new "procedural" tree type for linear step-by-step project workflows
(domain controller setup, M365 onboarding, VPN config, etc). Includes intake
form builder, two-panel step navigation, variable resolution, procedural
exports, 3 seed templates, and UI rename from "Trees" to "Flows".

Also archives 19 implemented plan docs and creates deferred features backlog.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/router.tsx

@@ -19,6 +19,8 @@ const TreeLibraryPage = lazy(() => import('@/pages/TreeLibraryPage'))
 const MyTreesPage = lazy(() => import('@/pages/MyTreesPage'))
 const TreeNavigationPage = lazy(() => import('@/pages/TreeNavigationPage'))
 const TreeEditorPage = lazy(() => import('@/pages/TreeEditorPage'))
+const ProceduralEditorPage = lazy(() => import('@/pages/ProceduralEditorPage'))
+const ProceduralNavigationPage = lazy(() => import('@/pages/ProceduralNavigationPage'))
 const SessionHistoryPage = lazy(() => import('@/pages/SessionHistoryPage'))
 const SessionDetailPage = lazy(() => import('@/pages/SessionDetailPage'))
 const AccountSettingsPage = lazy(() => import('@/pages/AccountSettingsPage'))
@@ -127,6 +129,30 @@ export const router = createBrowserRouter([
           </Suspense>
         ),
       },
+      {
+        path: 'flows/new',
+        element: (
+          <Suspense fallback={<PageLoader />}>
+            <ProceduralEditorPage />
+          </Suspense>
+        ),
+      },
+      {
+        path: 'flows/:id/edit',
+        element: (
+          <Suspense fallback={<PageLoader />}>
+            <ProceduralEditorPage />
+          </Suspense>
+        ),
+      },
+      {
+        path: 'flows/:id/navigate',
+        element: (
+          <Suspense fallback={<PageLoader />}>
+            <ProceduralNavigationPage />
+          </Suspense>
+        ),
+      },
       {
         path: 'trees/:id/navigate',
         element: (