fix: navigation correctness - back buttons, exit dialog, dedup nav, redirects

- Standardize all procedural back/exit paths to /trees (not /my-trees)
- Add exit button with ConfirmDialog to procedural session top bar
- Consolidate duplicate account links in sidebar and topbar
- Auto-redirect non-owners to personal analytics
- Add toast feedback before silent permission redirects in tree editor
- Delete orphaned AdminCategoriesPage

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

frontend/src/pages/ProceduralEditorPage.tsx

@@ -83,13 +83,13 @@ export function ProceduralEditorPage() {
       const tree = await treesApi.get(treeId)
       if (tree.tree_type !== 'procedural' && tree.tree_type !== 'maintenance') {
         toast.error('This flow is not a procedural or maintenance flow')
-        navigate('/my-trees')
+        navigate('/trees')
         return
       }
       loadTree(tree)
     } catch {
       toast.error('Failed to load flow')
-      navigate('/my-trees')
+      navigate('/trees')
     }
   }
 
@@ -154,7 +154,7 @@ export function ProceduralEditorPage() {
       <div className="flex shrink-0 items-center justify-between border-b border-border bg-card px-4 py-2">
         <div className="flex items-center gap-3">
           <button
-            onClick={() => navigate('/my-trees')}
+            onClick={() => navigate('/trees')}
             className="rounded-md p-2 text-muted-foreground hover:bg-accent hover:text-foreground"
           >
             <ArrowLeft className="h-5 w-5" />