feat(guides): rewrite in-product User Guides as Diátaxis how-tos

Replace 15 feature-dump guides with 43 problem-oriented how-tos grouped
under 10 categories. Drop Maintenance Flows / AI Assistant / Flow Assist
Sparkles — those surfaces no longer exist post-FlowPilot pivot. Rename
Step Library → Solutions Library throughout. Correct every "click X in
the sidebar" reference to match live labels (Home, History, Tickets,
Flows, Scripts, Data, Acct).

Schema: add `category: CategoryId` and optional `relatedSlugs` to Guide;
new Category type and `categories` const drive hub ordering. GuidesHubPage
renders category sections (auto-hides empty); GuideDetailPage renders a
related-guides footer when set; GuideCard drops the misleading "N sections"
subtitle.

Fix step.tip markdown rendering — `**bold**` rendered literally because
tip used plain text instead of the same regex replacement used on
instruction.

14 net-new how-tos for FlowPilot-era surfaces with no prior coverage:
tasklane keyboard flow, view-what-we-know, ask-AI mid-session,
pause-and-leave, resolve, record-fix-outcome, escalate (Escalation
Mode), post-docs-to-ticket, send-client-update, build-script-from-scratch,
open-suggested-flow, pin-a-flow, invite-teammate.

Browser-verified against engineer + owner test users (sidebar labels,
account sub-pages, pilot-screen header buttons, Tasks panel, integration
form). tsc clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/guides/GuideCard.tsx

@@ -24,9 +24,6 @@ export function GuideCard({ guide }: GuideCardProps) {
           <p className="text-xs text-muted-foreground leading-relaxed">
             {guide.summary}
           </p>
-          <span className="mt-2 inline-block font-sans text-[0.625rem] uppercase tracking-widest text-primary">
-            {guide.sections.length} {guide.sections.length === 1 ? 'section' : 'sections'}
-          </span>
         </div>
       </div>
     </Link>

frontend/src/components/guides/GuideSection.tsx

@@ -37,7 +37,12 @@ export function GuideSection({ section, index }: GuideSectionProps) {
               <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}
+                  <span className="font-semibold text-foreground">Tip:</span>{' '}
+                  <span
+                    dangerouslySetInnerHTML={{
+                      __html: step.tip.replace(/\*\*(.*?)\*\*/g, '<strong class="text-foreground font-semibold">$1</strong>'),
+                    }}
+                  />
                 </p>
               </div>
             )}