feat: implement My Trees, admin UI, rating modal, and bundle optimization (Issues #15, #18, #19, #31)

Frontend features:
- My Trees personal dashboard with fork tracking (Issue #15)
- Tree sharing UI with token generation and copy (Issue #16)
- Draft tree badges and validation UI (Issue #25)
- Save session as tree modal (Issue #17)
- Rate/review modal with localStorage tracking (Issue #19)
- Admin category management with drag-and-drop (Issue #18)
- Bundle size optimization with code splitting (Issue #31)

Components created:
- MyTreesPage: Personal tree organization
- AdminCategoriesPage: Category CRUD with @dnd-kit
- ShareTreeModal: Tree sharing interface
- SaveSessionAsTreeModal: Session conversion UI
- StepRatingModal: Post-session rating with stars
- StarRating: Reusable rating component
- PageLoader: Loading fallback for lazy routes
- CreateCategoryModal, EditCategoryModal: Admin modals

Bundle optimization:
- Reduced from 892 KB to 221 KB (75% reduction)
- Dynamic imports for 9 heavy pages
- Vendor chunk splitting for optimal caching
- 6 separate vendor chunks (react, markdown, utils, dnd, icons, state)

Dependencies added:
- @dnd-kit/core, @dnd-kit/sortable, @dnd-kit/utilities

API clients:
- stepCategories: Full CRUD for admin
- Enhanced sessions: saveAsTree endpoint
- Enhanced trees: share, fork, canPublish endpoints

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/components/library/TreeTableView.tsx

@@ -1,6 +1,6 @@
 import { useState } from 'react'
 import { Link } from 'react-router-dom'
-import { Pencil, Globe, Lock, ChevronUp, ChevronDown } from 'lucide-react'
+import { Pencil, Globe, Lock, ChevronUp, ChevronDown, GitBranch, FileText } from 'lucide-react'
 import type { TreeListItem } from '@/types'
 import { TagBadges } from '@/components/common/TagBadges'
 import { AddToFolderMenu } from './AddToFolderMenu'
@@ -14,6 +14,7 @@ interface TreeTableViewProps {
   onFolderCreated: (parentId?: string | null) => void
   onDeleteTree: (tree: TreeListItem) => void
   onSortChange?: (sortBy: string) => void
+  onForkTree?: (treeId: string) => void
 }
 
 type SortColumn = 'name' | 'category' | 'version' | 'usage' | 'updated'
@@ -24,6 +25,7 @@ export function TreeTableView({
   onTagClick,
   onFolderCreated,
   onSortChange,
+  onForkTree,
 }: TreeTableViewProps) {
   const { canEditTree } = usePermissions()
   const [sortColumn, setSortColumn] = useState<SortColumn | null>(null)
@@ -135,6 +137,12 @@ export function TreeTableView({
                   <span className="font-medium text-card-foreground truncate max-w-[200px]">
                     {tree.name}
                   </span>
+                  {tree.status === 'draft' && (
+                    <span className="inline-flex items-center gap-1 rounded-full bg-yellow-100 px-2 py-0.5 text-xs font-medium text-yellow-800 dark:bg-yellow-900/30 dark:text-yellow-400 flex-shrink-0">
+                      <FileText className="h-3 w-3" />
+                      Draft
+                    </span>
+                  )}
                   {tree.is_public ? (
                     <span title="Public tree">
                       <Globe className="h-3.5 w-3.5 text-muted-foreground flex-shrink-0" />
@@ -175,6 +183,19 @@ export function TreeTableView({
               <td className="px-4 py-3">
                 <div className="flex items-center justify-end gap-2">
                   <AddToFolderMenu treeId={tree.id} onFolderCreated={onFolderCreated} />
+                  {onForkTree && (
+                    <button
+                      type="button"
+                      onClick={() => onForkTree(tree.id)}
+                      className={cn(
+                        'rounded-md border border-input p-1.5 text-muted-foreground',
+                        'hover:bg-accent hover:text-accent-foreground'
+                      )}
+                      title="Fork tree"
+                    >
+                      <GitBranch className="h-3.5 w-3.5" />
+                    </button>
+                  )}
                   {canEditTree({ author_id: tree.author_id, account_id: tree.account_id }) && (
                     <Link
                       to={`/trees/${tree.id}/edit`}