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/react/rules/rendering-hydration-no-flicker.md

@@ -0,0 +1,82 @@
+---
+title: Prevent Hydration Mismatch Without Flickering
+impact: MEDIUM
+impactDescription: avoids visual flicker and hydration errors
+tags: rendering, ssr, hydration, localStorage, flicker
+---
+
+## Prevent Hydration Mismatch Without Flickering
+
+When rendering content that depends on client-side storage (localStorage, cookies), avoid both SSR breakage and post-hydration flickering by injecting a synchronous script that updates the DOM before React hydrates.
+
+**Incorrect (breaks SSR):**
+
+```tsx
+function ThemeWrapper({ children }: { children: ReactNode }) {
+  // localStorage is not available on server - throws error
+  const theme = localStorage.getItem('theme') || 'light'
+  
+  return (
+    <div className={theme}>
+      {children}
+    </div>
+  )
+}
+```
+
+Server-side rendering will fail because `localStorage` is undefined.
+
+**Incorrect (visual flickering):**
+
+```tsx
+function ThemeWrapper({ children }: { children: ReactNode }) {
+  const [theme, setTheme] = useState('light')
+  
+  useEffect(() => {
+    // Runs after hydration - causes visible flash
+    const stored = localStorage.getItem('theme')
+    if (stored) {
+      setTheme(stored)
+    }
+  }, [])
+  
+  return (
+    <div className={theme}>
+      {children}
+    </div>
+  )
+}
+```
+
+Component first renders with default value (`light`), then updates after hydration, causing a visible flash of incorrect content.
+
+**Correct (no flicker, no hydration mismatch):**
+
+```tsx
+function ThemeWrapper({ children }: { children: ReactNode }) {
+  return (
+    <>
+      <div id="theme-wrapper">
+        {children}
+      </div>
+      <script
+        dangerouslySetInnerHTML={{
+          __html: `
+            (function() {
+              try {
+                var theme = localStorage.getItem('theme') || 'light';
+                var el = document.getElementById('theme-wrapper');
+                if (el) el.className = theme;
+              } catch (e) {}
+            })();
+          `,
+        }}
+      />
+    </>
+  )
+}
+```
+
+The inline script executes synchronously before showing the element, ensuring the DOM already has the correct value. No flickering, no hydration mismatch.
+
+This pattern is especially useful for theme toggles, user preferences, authentication states, and any client-only data that should render immediately without flashing default values.