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/kb-accelerator/SourcePanel.tsx

@@ -0,0 +1,42 @@
+import { useMemo } from 'react'
+import { FileText } from 'lucide-react'
+
+interface SourcePanelProps {
+  sourceText: string
+  sourceFormat: string
+  highlightExcerpt: string | null
+}
+
+export function SourcePanel({ sourceText, sourceFormat, highlightExcerpt }: SourcePanelProps) {
+  const renderedText = useMemo(() => {
+    if (!highlightExcerpt || !sourceText.includes(highlightExcerpt)) {
+      return <span>{sourceText}</span>
+    }
+
+    const idx = sourceText.indexOf(highlightExcerpt)
+    return (
+      <>
+        <span>{sourceText.slice(0, idx)}</span>
+        <mark className="bg-primary/20 text-foreground rounded px-0.5">{highlightExcerpt}</mark>
+        <span>{sourceText.slice(idx + highlightExcerpt.length)}</span>
+      </>
+    )
+  }, [sourceText, highlightExcerpt])
+
+  return (
+    <div className="glass-card-static flex flex-col h-full">
+      <div className="flex items-center gap-2 px-4 py-3 border-b" style={{ borderColor: 'var(--glass-border)' }}>
+        <FileText size={16} className="text-muted-foreground" />
+        <span className="text-sm font-medium text-foreground">Source Document</span>
+        <span className="font-label text-[0.625rem] uppercase tracking-[0.1em] text-muted-foreground ml-auto">
+          {sourceFormat}
+        </span>
+      </div>
+      <div className="flex-1 overflow-y-auto p-4">
+        <pre className="text-sm text-muted-foreground whitespace-pre-wrap font-sans leading-relaxed">
+          {renderedText}
+        </pre>
+      </div>
+    </div>
+  )
+}