Fix: shared events duplication

[abdullai-t]

Summary / Highlights

This PR fixes the duplication of shared events on the admin portal.

When retrieving events visible to a community admin, the backend was fetching all events created by the admin's community as well as those shared with the admin's community. This led to duplication because the concatenation of these two sets of events did not enforce uniqueness.

The changes implemented in this PR ensure that only unique events are displayed to the community admin by calling .distinct() on the final events set.

Details (Give details about what this PR accomplishes, include any screenshots etc)

Testing Steps (Provide details on how your changes can be tested)

Requirements (place an x in each [ ])

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've tested my changes manually.
• I've added unit tests to my PR.

Transparency (Project board)

• I've given my PR a meaningful title.
• I linked this PR to the relevant issue.
• I moved the linked issue from the "Sprint backlog" to "In progress" when I started this.
• I moved the linked issue to "QA Verification" now that it is ready to merge.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 58.76%. Comparing base (b64feba) to head (b837633).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/api/store/event.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1197      +/-   ##
==========================================
- Coverage   58.77%   58.76%   -0.02%     
==========================================
  Files         501      501              
  Lines       37364    37364              
==========================================
- Hits        21961    21956       -5     
- Misses      15403    15408       +5     

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[frimpongopoku]

LGTM