Revamp Get Started section

[scott-klaytn]

✨ Proposed Changes

Overhauled the Get Started section to improve developer onboarding clarity and streamline the early setup experience.

• Redesigned and expanded the Get Started page for better guidance.
• Restructured entries under the Get Started category for a more logical flow.
• Moved and consolidated the existing Account section (previously under Get Started) into Nodes → Endpoint Node → ken CLI Commands, since account management via CLI is an advanced topic more relevant for node operators and infrastructure, not general onboarding.

🗂️ Types of changes

• Minor Issues and Typos
• Major Content Contribution
• Others (e.g. platform-specific changes)

✅ Checklist

• I have read the CONTRIBUTING GUIDELINES.
• If following Standard Workflow: I have linked the approved issue below.
• If submitting without a prior issue (Maintainer/Regular): I have provided detailed context in the "Proposed Changes" section above.
• My changes render correctly (if applicable, run npm run build locally).
• I have added necessary documentation updates (if appropriate).
• Any dependent changes have been merged and published.

📌 Related issues

💡 Further comments