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/ui-ux-design-user-experience/references/14-design-handoff--collaboration.md

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+
+### Design Specs
+
+**What to Include:**
+- Component dimensions and spacing
+- Color values (HEX, RGB, HSL)
+- Typography specs (font, size, weight, line height)
+- States (default, hover, active, disabled, focus)
+- Responsive behavior documentation
+- Animation specifications
+
+### Developer Handoff
+
+**Tools:** Figma Inspect, Zeplin, Avocode
+
+**Best Practices:**
+- Use consistent naming conventions
+- Organize components in logical groups
+- Document interactions and edge cases
+- Include assets in multiple formats
+- Provide responsive guidelines
+
+### Design-to-Code
+
+**Tools:** Figma to code plugins, Anima, Locofy
+
+**Limitations:**
+- Generated code often needs refinement
+- Complex interactions require manual coding
+- Accessibility may need additional work
+
+**Best Use:** Rapid prototyping, simple components
+
+### Collaboration
+
+**Design Reviews:**
+- Regular critiques with team
+- Structured feedback sessions
+- Document decisions and rationale
+
+**Version Control:**
+- Use branching in design tools
+- Document version history
+- Maintain single source of truth
+
+---