Add Jekyll multilingual structure

[taherdhanera]

/claim #2

Fixes #2

Summary

• add a reusable language map in _config.yml
• add localized UI copy in _data/i18n.yml
• add a language switcher include and header styling
• filter the home page by lang so translated posts do not appear on the English index
• add Spanish localized home/about pages and one translated post in root _posts/ with a Spanish permalink to establish the pattern for additional languages
• document how to add future languages in the README

Verification

• git diff --check
• inspected localized file layout under es/, _data/, _includes/, and _posts/

Note: I could not run bundle exec jekyll build in this Windows environment because Ruby/Bundler are not installed (bundle and ruby commands are unavailable).

[taherdhanera]

PR-side status refresh after newer same-issue #2 activity.

My active multilingual Jekyll bounty submission remains this earlier PR #11: #11
Latest issue-side protection note: #2 (comment)

Current contributor-side status re-verified now:

• PR Add Jekyll multilingual structure #11 is open and non-draft
• PR Add Jekyll multilingual structure #11 is CLEAN/mergeable
• PR body includes /claim #2 and Fixes #2
• no CI checks are currently reported on this branch
• no maintainer-requested changes or contributor-side WIP are pending from me

Newer PR #17 is adjacent same-issue activity and does not replace the earlier active issue #2 bounty submission on PR #11.