Revamps build/index

[dawnkelly09]

Description

Please explain the changes this PR addresses here.

• adds copy to the build/index page to guide the user journey
• renames the rendered title to Build Multichain
• adds links for pending Product Comparison Guide and Use Cases pages/sections
• removes the navigation cards
• renames "Build Frontend Applications" nav heading/section name to "Application Toolkit"
• renames "Build Contract Integrations" nav heading/section name to "Transfer Protocols"
  Note: I did not update file/directory names yet until we know if/how much of this we want to implement

Things remaining to address (not changed with this PR):

• I would like to remove the current Toolkit section based on:
  • Wormhole scan entry is just a link, not even a page
  • Wormhole SDK nav entry is duplicated and links to the same pages in the Application Toolkit section
  • The Solidity SDK page makes more sense being in Transfer Protocols where the smart contract guides live
  • The FAQs here would be better served moving to the section to which they pertain and/or adding to existing FAQ page
  • Tilt page should move to Start Building section as it dev env setup materials
  • Move Wormhole CLI to Start Building section as it is for all types of WH builders to use
  • Wormhole Spy SDK link on card can move to Related Resources on Spy page
  • VAA Parser card can be a Related Resource on VAA page

Checklist

• [x ] Required - I have added a label to this PR 🏷️
• [x ] Required - I have run my changes through Grammarly
• If pages have been moved, I have created redirects in the wormhole-mkdocs repo - I didn't move anything. Yet!

[dawnkelly09]

Closing as these items are covered in the new IA PRs