feat: UI design system - sidebar layout, workspace system, and shell redesign (#77)

* feat: add workspace system and sidebar layout (UI design system Phase A+B)

Backend: Workspace model, migration (036), schemas, CRUD API endpoints.
Adds workspace_id to trees and categories, seeds 4 default workspaces
per account, auto-assigns existing trees by tree_type.

Frontend: Complete AppLayout rewrite from top-nav to CSS Grid shell
with persistent sidebar + topbar. New components: WorkspaceSwitcher,
NavItem, CategoryList, TagCloud, TopBar, Sidebar. Dashboard components:
QuickStats, FiltersBar, SectionGroup, TreeListItem, SessionsPanel.
WorkspaceStore with localStorage persistence.

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

* feat: add command palette search, dashboard rewrite, and shell height fixes (Phase C)

- Add ⌘K command palette with debounced search across flows and sessions
- Rewrite QuickStartPage as dashboard with stats, filters, sessions panel
- Fix h-[calc(100vh-4rem)] → h-full across all pages for CSS Grid shell
- Add active session count badge to sidebar Sessions nav item

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

* feat: add sidebar collapse, category/tag filtering, and workspace CRUD (Phase D)

- Sidebar collapse/expand toggle with icon-only rail mode (persisted)
- Sidebar category/tag clicks navigate to /trees with URL params
- TreeLibraryPage syncs filters from URL search params bidirectionally
- Workspace create modal with icon picker and auto-slug generation
- TopBar logo adapts to collapsed sidebar state

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

* feat: add Quick Launch modal with actions and recent flows

- Zap button opens Quick Launch with create/navigate shortcuts
- Shows recent flows for quick session start
- Keyboard navigation support (arrows + enter)

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

* feat: add activity notifications panel with session feed

- Bell icon shows dot indicator for recent activity
- Dropdown panel shows recent sessions with status icons
- Links to session detail and sessions list page

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

* feat: remove workspace system, add pinned flows and label renames

Replace workspace system with pinned flows API (pin/unpin/list/reorder).
Rename user-facing labels: Tree→Flow, Procedure→Project. Add sidebar
nav sub-items for flow type filtering. Remove 11 workspace files,
add migrations 037-038, clean all workspace references.

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

* fix: collapsed sidebar layout scaling and toggle button size

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

* refactor: migrate auth pages to new design system

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

* refactor: migrate TreeLibraryPage to new design system

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

* refactor: migrate session pages to new design system

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

* refactor: migrate TreeEditorPage to new design system

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

* refactor: migrate TreeNavigationPage to new design system

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

* refactor: migrate session sharing components to new design system

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

* chore: remove workspace dropdown animation (dead code)

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

* refactor: migrate common components to new design system

Migrate 15 components from monochrome glass-card design to purple gradient
accent design system tokens (bg-card, border-border, text-foreground,
bg-gradient-brand, etc.)

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

* refactor: migrate procedural and step library components to new design system

Migrate 10 components from monochrome glass-card design to purple gradient
accent design system tokens.

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

* refactor: migrate admin pages and components to new design system

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

* refactor: migrate remaining pages to new design system

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

* refactor: migrate remaining components to new design system

Migrates 38 files: tree-editor forms, session modals, step library,
common components, library views, tree preview, and misc UI to use
design tokens (bg-card, border-border, text-foreground, bg-accent,
bg-gradient-brand) replacing old monochrome patterns.

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

* fix: keep brand text visible on sidebar collapse, hide sub-items until hover

- TopBar: always show "ResolutionFlow" text regardless of sidebar state
- NavItem: sub-items (Troubleshooting, Projects) hidden by default,
  revealed on hover or when a child route is active

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/api/index.ts

@@ -11,3 +11,4 @@ export { default as stepCategoriesApi } from './stepCategories'
 export { default as accountsApi } from './accounts'
 export { default as adminApi } from './admin'
 export { treeMarkdownApi } from './treeMarkdown'
+export { default as pinnedFlowsApi } from './pinnedFlows'

frontend/src/api/pinnedFlows.ts

@@ -0,0 +1,40 @@
+import { apiClient } from './client'
+
+export interface PinnedFlow {
+  id: string
+  tree_id: string
+  tree_name: string
+  tree_type: 'troubleshooting' | 'procedural'
+  category_emoji?: string
+  category_name?: string
+  pinned_at: string
+  display_order: number
+}
+
+export interface PinnedFlowsResponse {
+  items: PinnedFlow[]
+  count: number
+}
+
+export const pinnedFlowsApi = {
+  list: async (): Promise<PinnedFlowsResponse> => {
+    const { data } = await apiClient.get('/trees/pinned')
+    return data
+  },
+
+  pin: async (treeId: string): Promise<PinnedFlow> => {
+    const { data } = await apiClient.post(`/trees/${treeId}/pin`)
+    return data
+  },
+
+  unpin: async (treeId: string): Promise<void> => {
+    await apiClient.delete(`/trees/${treeId}/pin`)
+  },
+
+  reorder: async (order: { tree_id: string; display_order: number }[]): Promise<PinnedFlowsResponse> => {
+    const { data } = await apiClient.patch('/trees/pinned/reorder', { order })
+    return data
+  },
+}
+
+export default pinnedFlowsApi