feat: add account management, email verification, AI fixes, and user guides

- Profile settings, account transfer, delete/leave account flows
- Email verification with JWT tokens and Resend integration
- AI assistant/copilot fixes: markdown rendering, shared RAG helpers,
  token tracking, input refocus, model_validate usage
- User guides hub + detail pages with 13 topic guides
- Sidebar and top bar navigation for guides

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

frontend/src/components/guides/GuideSection.tsx

@@ -0,0 +1,49 @@
+import { Lightbulb } from 'lucide-react'
+import type { GuideSection as GuideSectionType } from '@/data/guides'
+
+interface GuideSectionProps {
+  section: GuideSectionType
+  index: number
+}
+
+export function GuideSection({ section, index }: GuideSectionProps) {
+  return (
+    <div className="mb-8">
+      <h3 className="text-base font-heading font-semibold text-foreground mb-4 flex items-center gap-2">
+        <span className="flex h-6 w-6 shrink-0 items-center justify-center rounded-md bg-primary/10 text-xs font-bold text-primary">
+          {index + 1}
+        </span>
+        {section.title}
+      </h3>
+      <ol className="space-y-3 pl-8">
+        {section.steps.map((step, i) => (
+          <li key={i} className="relative">
+            <span className="absolute -left-6 top-0.5 font-label text-[0.625rem] text-muted-foreground">
+              {i + 1}.
+            </span>
+            <p
+              className="text-sm text-foreground leading-relaxed"
+              dangerouslySetInnerHTML={{
+                __html: step.instruction
+                  .replace(/\*\*(.*?)\*\*/g, '<strong class="text-foreground font-semibold">$1</strong>')
+              }}
+            />
+            {step.detail && (
+              <p className="mt-1 text-xs text-muted-foreground leading-relaxed">
+                {step.detail}
+              </p>
+            )}
+            {step.tip && (
+              <div className="mt-2 flex items-start gap-2 rounded-lg bg-primary/5 border-l-2 border-primary px-3 py-2">
+                <Lightbulb size={14} className="text-primary shrink-0 mt-0.5" />
+                <p className="text-xs text-muted-foreground leading-relaxed">
+                  <span className="font-semibold text-foreground">Tip:</span> {step.tip}
+                </p>
+              </div>
+            )}
+          </li>
+        ))}
+      </ol>
+    </div>
+  )
+}