docs: add comprehensive frontend landing page plan and download design skills

Add detailed landing page development plan in docs/frontend_landing_plan.md:
- Complete landing page structure (Hero, Problem/Solution, Features, Demo, CTA)
- Design guidelines from downloaded skills (typography, color, motion, composition)
- Security considerations (XSS prevention, input sanitization, CSP)
- Performance targets (LCP <2.5s, bundle <150KB, Lighthouse >90)
- Responsiveness and accessibility requirements (WCAG 2.1 AA)
- Success KPIs and monitoring setup
- 3-week development timeline with daily tasks
- Definition of Done checklist

Download 10+ frontend/UI/UX skills via universal-skills-manager:
- frontend-ui-ux: UI/UX design without mockups
- frontend-design-guidelines: Production-grade interface guidelines
- frontend-developer: React best practices (40+ rules)
- frontend-engineer: Next.js 14 App Router patterns
- ui-ux-master: Comprehensive design systems and accessibility
- ui-ux-systems-designer: Information architecture and interaction
- ui-ux-design-user-experience: Platform-specific guidelines
- Plus additional reference materials and validation scripts

Configure universal-skills MCP with SkillsMP API key for curated skill access.

Safety first: All skills validated before installation, no project code modified.

Refs: Universal Skills Manager (github:jacob-bd/universal-skills-manager)
Next: Begin Sprint 3 landing page development

.opencode/skills/frontend-developer/react/rules/rerender-memo.md

@@ -0,0 +1,44 @@
+---
+title: Extract to Memoized Components
+impact: MEDIUM
+impactDescription: enables early returns
+tags: rerender, memo, useMemo, optimization
+---
+
+## Extract to Memoized Components
+
+Extract expensive work into memoized components to enable early returns before computation.
+
+**Incorrect (computes avatar even when loading):**
+
+```tsx
+function Profile({ user, loading }: Props) {
+  const avatar = useMemo(() => {
+    const id = computeAvatarId(user)
+    return <Avatar id={id} />
+  }, [user])
+
+  if (loading) return <Skeleton />
+  return <div>{avatar}</div>
+}
+```
+
+**Correct (skips computation when loading):**
+
+```tsx
+const UserAvatar = memo(function UserAvatar({ user }: { user: User }) {
+  const id = useMemo(() => computeAvatarId(user), [user])
+  return <Avatar id={id} />
+})
+
+function Profile({ user, loading }: Props) {
+  if (loading) return <Skeleton />
+  return (
+    <div>
+      <UserAvatar user={user} />
+    </div>
+  )
+}
+```
+
+**Note:** If your project has [React Compiler](https://react.dev/learn/react-compiler) enabled, manual memoization with `memo()` and `useMemo()` is not necessary. The compiler automatically optimizes re-renders.