Enhance Engine API page with structural clarity and summary table

[alok-108]

This PR enhances the recently added Engine API page (originally from #494, related to #435) by:

• Adding a concise introduction and a quick-reference Key Methods table.
• Reorganizing content into distinct, highly scannable sections (Authentication, Core Methods, Validator Flow, etc.)
• Structuring the Validator Flow into clear numbered steps.
• Adding contextual links to the latest community roadmap framework (Strawmap).

This builds on the great work by @ArshLabs to make the page even more readable and accessible for newcomers to the Ethereum client architecture.

[github-actions]

Hi @alok-108,

⚠️ Potential typos found in your pull request:

• 📄 ./docs/wiki/EL/engine-api.md (line(s) 237,275):
  1. ❌ Strawmap
• 📄 ./docs/wiki/EL/engine-api.md (line(s) 237,275):
  1. ❌ Strawmap
• 📄 ./docs/wiki/research/history-expiry/history-expiry.md (line(s) 37,39):
  1. ❌ bitmask
• 📄 ./docs/wiki/research/history-expiry/history-expiry.md (line(s) 37,39):
  1. ❌ bitmask
• 📄 ./docs/wiki/CL/cl-networking.md (line(s) 251):
  1. ❌ decrypt

ℹ️ How to fix this error:

1. If these are actual typos:

   • Open the files at the specified line numbers and fix them

2. If these are names or one-off nouns:

   • Wrap them in <name> tags
   • Example: <name>Alex Pereira</name>
   • Use this for people's names or unique terms that appear rarely

3. If these are valid terms:

   • Add them to wordlist.txt (one word per line)
   • Terms must be plain text without spaces/special chars
   • The list is case-insensitive

4. If these are code terms:

   • Wrap them in backticks (`) in your markdown

ℹ️ Checking for typos locally

1. Install aspell for your platform
2. Navigate to project root and run:

for f in **/*.md ; do echo $f ; aspell --lang=en_US --mode=markdown --home-dir=. --personal=wordlist.txt --ignore-case=true --camel-case --add-sgml-skip nospellcheck list < $f | sort | uniq -c ; done

Learn more about wordlist format