Update landing page for agentic development

[AvdLee]

Summary

• Refresh the homepage hero around modern iOS development for developers and AI coding agents.
• Add Agentic Development as the first homepage feature and a dedicated /features/agentic-development/ category.
• Add the compressed CLI + Agent Skill demo video and modernize Network Monitor / capture feature copy.

Test plan

• npm run lint
• npm run format:check
• npm run typecheck
• npm run build
• npm run knip
• Opened http://localhost:4322/, http://localhost:4322/features/, and http://localhost:4322/features/agentic-development/