feat: KB Accelerator — convert KB articles into interactive flows

Full-stack implementation of the KB Accelerator feature that converts
static MSP knowledge base articles into interactive troubleshooting
and procedural flows using AI.

Backend:
- Migrations 054/055: kb_imports, kb_import_nodes tables + plan_limits KB columns
- SQLAlchemy models with relationships and self-referential node hierarchy
- Text extraction service (txt, paste, docx with structural metadata)
- AI conversion service with MSP-specialist prompts for both flow types
- 8 API endpoints: upload, get, list, convert, edit node, commit, delete, quota
- Tier-gated access via plan_limits (free: 3 lifetime, pro/team: unlimited)
- 8 integration tests covering upload, get/list, quota, commit, delete

Frontend:
- TypeScript types and API client for all KB Accelerator endpoints
- Multi-step wizard page: upload → processing → review → success
- Upload screen with paste/file tabs, drag-drop, target type selector
- Two-panel review screen with source highlighting and node cards
- Per-node actions: approve, edit, regenerate, insert, delete
- Confidence color indicators (green/amber/red)
- Sidebar navigation with Sparkles icon
- Code-split lazy-loaded route at /kb-accelerator

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

frontend/src/components/layout/Sidebar.tsx

@@ -1,5 +1,5 @@
 import { useEffect, useState } from 'react'
-import { LayoutGrid, Box, PenLine, Clock, FileText, Bookmark, BarChart3, Settings, PanelLeftClose, PanelLeftOpen, MessageSquareText, BotMessageSquare, BookOpen } from 'lucide-react'
+import { LayoutGrid, Box, PenLine, Clock, FileText, Bookmark, BarChart3, Settings, PanelLeftClose, PanelLeftOpen, MessageSquareText, BotMessageSquare, BookOpen, Sparkles } from 'lucide-react'
 import { cn } from '@/lib/utils'
 import { useUserPreferencesStore } from '@/store/userPreferencesStore'
 import { usePinnedFlowsStore } from '@/store/pinnedFlowsStore'
@@ -83,6 +83,7 @@ export function Sidebar() {
             <NavItem href="/shares" icon={FileText} label="Exports" collapsed />
             <NavItem href="/assistant" icon={BotMessageSquare} label="AI Assistant" collapsed />
             <NavItem href="/step-library" icon={Bookmark} label="Step Library" collapsed />
+            <NavItem href="/kb-accelerator" icon={Sparkles} label="KB Accelerator" collapsed />
             <NavItem href="/analytics" icon={BarChart3} label="Analytics" collapsed />
             <NavItem href="/guides" icon={BookOpen} label="User Guides" collapsed />
             <NavItem href="/feedback" icon={MessageSquareText} label="Feedback" collapsed />
@@ -115,6 +116,7 @@ export function Sidebar() {
             <NavItem href="/shares" icon={FileText} label="Exports" />
             <NavItem href="/assistant" icon={BotMessageSquare} label="AI Assistant" />
             <NavItem href="/step-library" icon={Bookmark} label="Step Library" />
+            <NavItem href="/kb-accelerator" icon={Sparkles} label="KB Accelerator" />
             <NavItem href="/analytics" icon={BarChart3} label="Analytics" />
           </div>
         </>