refactor: consolidate Algolia search into external js/algolia-search.js

[Parth-Garg2629]

Problem

The Algolia search logic existed in two near-identical places:

• _includes/algolia.html — active inline implementation (~135 lines of JS in a template)
• js/algolia-search.js — unused duplicate

Solution

• _includes/algolia.html is now a thin config bridge only — it exposes Jekyll Liquid variables as window.ALGOLIA_CONFIG and loads the external JS file
• js/algolia-search.js is now the single implementation file — reads config from window.ALGOLIA_CONFIG, pure vanilla JS with no Liquid tags

Benefits

• ✅ Single source of truth for search logic
• ✅ External JS is browser-cacheable (inline scripts are not)
• ✅ Templates stay clean — no logic mixed into layout includes
• ✅ No YAML front matter tricks needed — config passes cleanly via a global

No functional changes

Search behaviour, styling, and UX are identical to before.
The 167 lines removed = the duplicate. The code that was identical in both files now lives in one place (
algolia-search.js). Nothing was deleted that wasn't already covered by the external file.

Closes #796