EDU-3945: landing pages redesign

[jsundai]

What does this PR do?

WIP

This PR implements a comprehensive redesign of Temporal's documentation landing pages, focusing on improved developer experience, modern design patterns, and streamlined onboarding flows.

Pages modified:
/ (Homepage)
/develop (Developer guide landing)
/develop/go, /develop/java, /develop/php, /develop/python, /develop/typescript, /develop/dotnet (SDK landing pages)
/develop/*/setup (New setup pages for all SDKs)
/introduction (Enhanced with new image assets and layout)
/features (Complete redesign)
/getting-started (Full revamp as new page)

Notes to reviewers

Summary of changes in this PR:
Landing Page Redesigns

• Homepage: Complete visual overhaul with new card-based layout, updated typography (Aeonik font family), and improved color scheme
• Developer Guide Landing Pages: Redesigned /develop section with cleaner card layouts and better content hierarchy
• SDK Landing Pages: Standardized design across Go, Java, PHP, Python, TypeScript, and .NET with:
  - New card-based layout replacing previous list format
  - Streamlined content focusing on titles and descriptions
• Getting Started Page: New page instead of redirect with gradient borders and improved CTAs

Interactive React Components

• Pattern Cards: Hover effects with subtle transforms and shadow changes
• CTA Sections: Interactive elements with gradient borders and hover states
• SDK Cards: Logo integration with proper spacing and hover interactions
• Navigation: Enhanced with new Ask AI button integration

Enhanced Developer Onboarding

• Setup Pages: Created dedicated setup/installation pages for all SDKs in two-column format
• Getting Started Flow: Redesigned with clear activity time badges (5min, 10min, 20min) and progressive disclosure
• Quick Start CTAs: Prominent "Create an account" and next page CTAs with gradient styling

Developer Experience Features

• Ask AI button on navbar: Added navbar button that integrates with existing Kapa AI widget: This is a custom React component with sparkle icon. Has responsive design (text on desktop, icon-only on mobile). Provides proper spacing and visual integration with existing navbar elements.