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/references/angular.md

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+# Modern Angular Architecture
+
+**Status**: Definitive Guide
+**Stack**: Angular 17+
+
+## 🏗 Architecture: Standalone & Zone-less
+
+### 1. Standalone Components
+
+- **Ban**: `NgModule` (unless for legacy libs).
+- **Enforce**: `standalone: true` in all components, directives, and pipes.
+- **Why**: Tree-shaking, easier testing, simplified learning curve.
+
+### 2. Signals (State Management)
+
+- **Signals over Observables**: Use Signals for synchronous state. Use RxJS ONLY for complex asynchronous event streams (debounce, switchMap).
+- **Ban**: `Zone.js` (eventually). Prepare for zoneless by using `ChangeDetectionStrategy.OnPush` everywhere.
+
+```typescript
+// ✅ GOOD: Signal
+@Component({ ... changeDetection: ChangeDetectionStrategy.OnPush })
+export class Counter {
+  count = signal(0);
+  double = computed(() => this.count() * 2);
+
+  increment() {
+    this.count.update(c => c + 1);
+  }
+}
+```
+
+### 3. Control Flow Syntax
+
+- **Use**: `@if`, `@for`, `@switch`.
+- **Ban**: `*ngIf`, `*ngFor` (legacy structural directives).
+
+## ⚡ Performance Patterns
+
+### 1. Deferrable Views
+
+- Use `@defer` to lazy load components without routing.
+- Criteria: `@defer (on viewport)` for below-the-fold content.
+
+### 2. Hydration
+
+- Enable Client Hydration in `app.config.ts`.
+- Avoid direct DOM manipulation which breaks hydration.
+
+## 🧪 Testing
+
+- **Harnesses**: Use Component Harnesses for robust tests.
+- **Signals**: Test signals by verifying computed outputs.