fix: username field is not populated by exact input

[MusaleTejas]

Description

This PR resolves the issue where the username field on the OneAccess dashboard does not display the exact username/login of the user, falling back instead to the prefix of their email address (email.split('@')[0]).

To address this, we now synchronize and store the actual WordPress user_login inside the sites_info JSON database field for each site, retrieve it during REST queries, and display the exact username in the frontend interface.

Changes

• Backend Syncing (inc/Modules/Rest/Actions_Controller.php): Included username in prepare_user_data and sanitized it in sanitize_user_data.
• Database Helper (inc/Modules/Core/DB.php): Added support for username inside sites_info JSON during user insertion, updates, and manually mapped users.
• REST Controller (inc/Modules/Rest/Governing_Site_Controller.php): Extracted the exact username from sites_info and exposed it at the user level in the get_users API response.
• Frontend Dashboard (assets/src/components/SharedUsers.tsx): Updated SharedUser interface and transformed the API response mapping to render user.username (with the email split as a fallback for legacy records).

[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 6.78%. Comparing base (d005570) to head (434209c).

Files with missing lines	Patch %	Lines
inc/Modules/Rest/Governing_Site_Controller.php	0.00%	10 Missing ⚠️
inc/Modules/Core/DB.php	0.00%	3 Missing ⚠️
inc/Modules/Rest/Actions_Controller.php	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              main    #145      +/-   ##
==========================================
- Coverage     6.81%   6.78%   -0.04%     
- Complexity     601     604       +3     
==========================================
  Files           20      20              
  Lines         3036    3050      +14     
==========================================
  Hits           207     207              
- Misses        2829    2843      +14     

Flag	Coverage Δ
unit	6.78% <0.00%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
inc/Modules/Rest/Actions_Controller.php	0.00% <0.00%> (ø)
inc/Modules/Core/DB.php	0.00% <0.00%> (ø)
inc/Modules/Rest/Governing_Site_Controller.php	0.00% <0.00%> (ø)

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