style(landing): update capabilities cards info and tags to match actual agent implementation

chore(ui): remove AI multi-agent subtitle from logo and core engine label from capabilities

style(frontend): prevent cutting off stats cards at bottom boundary by removing overflow-hidden and using min-h-screen

style(frontend): make background video page-wide and fixed for unified single-page layout

style(frontend): replace capabilities section background video with the bubble video

adapt Hero and Capabilities copy to match Agentic Investigation Core features

implement CapabilitiesSection component with icon cards grid

initialize React Vite frontend project with Tailwind v4 setup