refactor: consolidate Algolia search logic into algolia-search.js

[anuj452005]

Summary

Consolidates the Algolia search implementation into a single file,
eliminating duplicate logic between _includes/algolia.html and
js/algolia-search.js.

Problem

The search logic existed in two places:

• _includes/algolia.html — active inline implementation (used in production)
• js/algolia-search.js — unused external file with outdated logic

This violated the single source of truth principle, prevented browser
caching of the search JS, and added unnecessary complexity to the layout template.

Changes

• _includes/algolia.html: Reduced to a single <script src> tag
• js/algolia-search.js: Now the canonical implementation, updated with:
  • Dynamic keyboard shortcut placeholder (⌘K / Ctrl+K)
  • Escape-key handler (ported from the recent improvement in algolia.html)
  • Jekyll front matter for Liquid variable processing

No functional changes intended

Search behavior, keyboard shortcuts, and UI remain identical.
This is a structural refactor only.

Testing

• Site runs locally with bundle exec jekyll serve -l

closes #796