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/references/modern-signals.md

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+# Modern Signals & Fine-Grained Reactivity
+
+**Stack**: Svelte 5 (Runes), SolidJS, Qwik
+
+## 🧠 The Philosophy: "No Virtual DOM"
+
+Unlike React/Vue, these frameworks target the DOM directly.
+
+- **Fine-Grained**: Only the text node that changes updates. No component re-renders.
+- **Mental Model**: Code runs _once_ (setup), then reactivity takes over.
+
+## 🧱 Framework specifics
+
+### Svelte 5 (Runes)
+
+- **State**: `let count = $state(0)`
+- **Derived**: `let double = $derived(count * 2)`
+- **Side Effects**: `$effect(() => ...)`
+- **Snippets**: Replace slots with `{#snippet}`.
+
+### SolidJS
+
+- **Read/Write Split**: `const [count, setCount] = createSignal(0)`
+- **DOM Access**: strictly in `onMount`.
+- **Control Flow**: Use `<Show>`, `<For>` (don't use map).
+
+### Qwik (Resumability)
+
+- **The Golden Rule**: Do not execute JS on the client unless checking an event.
+- **Serialized State**: All state must be serializable (JSON).
+- **$**: The optimizer barrier. `onClick$`, `useSignal$`.
+
+## ⚡ Performance Targets
+
+1.  **Hydration**:
+    - **Svelte/Solid**: Fast hydration.
+    - **Qwik**: No hydration (Resumability).
+2.  **Closures**: Avoid creating closures in render loops (except Qwik where `$` handles it).
+
+## 🧪 Testing
+
+- **E2E**: Playwright is the gold standard for all three.
+- **Unit**: Vitest.