Add Academia.edu support to social media integrations (#3157)

## Description

This pull request adds support for Academia.edu profiles to the al-folio
social media integrations. Academia.edu is widely used by academics to
share and discover research,.

The changes are minimal and well-contained:
1. Added configuration options in socials.yml for Academia.edu with
organization and username fields
2. Updated social.liquid to handle the new social integration using the
Academicons font which already includes support for Academia.edu

## Changes

The implementation uses Academicons, which already includes the
Academia.edu icon (`ai-academia`), making this addition a natural fit
for the theme.

Unlike some other social media links that only require a single ID or
URL, Academia.edu profiles include both an organization (subdomain) and
a username in the format:
`https://[organization].academia.edu/[username]`. The implemented
solution supports this pattern by adding two parameters in the
socials.yml file.

## Why this is important

Academia.edu is a popular platform used by millions of researchers
worldwide to share their work. Adding support for it in the al-folio
theme aligns with the theme's academic focus and enhances its utility
for scholarly users. Many academics maintain both personal websites and
Academia.edu profiles, and being able to link between them provides
better visibility for their research.

The Academicons font already includes support for Academia.edu, so
adding this feature is a natural extension that makes use of existing
resources in the theme.

## Testing

The changes have been tested locally with a sample Academia.edu profile,
and the icon displays correctly alongside other social media icons. The
changes are minimal and don't affect any existing functionality.

## Screenshot

<img width="991" alt="image"
src="https://github.com/user-attachments/assets/15468b67-3002-44ce-aa25-22bc10766664"
/>

Author: Maclenn77

_data/socials.yml

@@ -2,6 +2,9 @@
 # the commented lines are the default social media links supported by the template
 # the socials will be displayed in the order they are defined here
 
+# academia_edu:  your organization and your username Ex. https://organization.academia.edu/UserName
+#  organization: princeton # your organization as appears in the subdomain
+#  username:  AlbertEinstein # your username
 # acm_id: # your dl.acm.org/profile/id
 # blogger_url: # your blogger URL
 # bluesky_url: # your bluesky URL

_includes/social.liquid

@@ -1,5 +1,7 @@
 {% for social in site.data.socials %}
   {% case social[0] %}
+    {% when 'academia_edu' %}
+      <a href="https://{{ social[1].organization }}.academia.edu/{{ social[1].username }}" title="Academia.edu"><i class="ai ai-academia"></i></a>
     {% when 'acm_id' %}
       <a href="https://dl.acm.org/profile/{{ social[1] }}/" title="ACM DL"><i class="ai ai-acm"></i></a>
     {% when 'blogger_url' %}