feat: add PSA ticket export format and Quick-Start landing page

PSA Export:
- New "PSA / Ticket Note" export format optimized for ConnectWise
- Structured output: Problem, Steps Taken, Resolution, Time Spent, Notes
- Prominent "Copy for Ticket" button on session detail page
- 24 unit tests for PSA export generator

Quick-Start Landing:
- New default landing page with search-first UX
- Auto-focused search bar with debounced tree search
- "Continue Session" cards for active sessions
- "Recent Trees" section from session history
- Home nav item and logo links updated

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

frontend/src/store/userPreferencesStore.ts

@@ -1,7 +1,7 @@
 import { create } from 'zustand'
 import { persist } from 'zustand/middleware'
 
-type ExportFormat = 'markdown' | 'text' | 'html'
+type ExportFormat = 'markdown' | 'text' | 'html' | 'psa'
 type TreeLibraryView = 'grid' | 'list' | 'table'
 type TreeSortBy = 'usage_count' | 'updated_at' | 'created_at' | 'name' | 'name_desc' | 'version'