fix: add type-aware routing for procedural flows

Centralizes tree navigation routing via getTreeNavigatePath helper.
Fixes all pages to route procedural sessions to /flows/:id/navigate
instead of /trees/:id/navigate. Adds safety redirect in troubleshooting
navigator and resume support in procedural navigator.

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

frontend/src/lib/routing.ts

@@ -0,0 +1,31 @@
+/**
+ * Shared routing helpers for tree/session navigation.
+ * Centralizes the logic for determining the correct navigation path
+ * based on tree type (troubleshooting vs procedural).
+ */
+
+/**
+ * Get the navigation path for starting or resuming a tree/session.
+ */
+export function getTreeNavigatePath(
+  treeId: string,
+  treeType?: string
+): string {
+  if (treeType === 'procedural') {
+    return `/flows/${treeId}/navigate`
+  }
+  return `/trees/${treeId}/navigate`
+}
+
+/**
+ * Get the editor path for a tree.
+ */
+export function getTreeEditorPath(
+  treeId: string,
+  treeType?: string
+): string {
+  if (treeType === 'procedural') {
+    return `/flows/${treeId}/edit`
+  }
+  return `/trees/${treeId}/edit`
+}