[PM-20554] fix admin endpoint for deleting unassigned items

[BTreston]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-20554

📔 Objective

This PR fixes an issue where you are unable to delete or restore unassigned items.

📸 Screenshots

Screen.Recording.2025-07-08.at.1.32.15.PM.mov

⏰ Reminders before review

• Contributor guidelines followed
• All formatters and local linters executed and passed
• Written new unit and / or integration tests where applicable
• Protected functional changes with optionality (feature flags)
• Used internationalization (i18n) for all UI strings
• CI builds passed
• Communicated to DevOps any deployment requirements
• Updated any necessary documentation (Confluence, contributing docs) or informed the documentation team

🦮 Reviewer guidelines

• 👍 (:+1:) or similar for great changes
• 📝 (:memo:) or ℹ️ (:information_source:) for notes or general info
• ❓ (:question:) for questions
• 🤔 (:thinking:) or 💭 (:thought_balloon:) for more open inquiry that's not quite a confirmed issue and could potentially benefit from discussion
• 🎨 (:art:) for suggestions / improvements
• ❌ (:x:) or ⚠️ (:warning:) for more significant problems or concerns needing attention
• 🌱 (:seedling:) or ♻️ (:recycle:) for future improvements or indications of technical debt
• ⛏ (:pick:) for minor or nitpick changes

[github-actions]

Checkmarx One – Scan Summary & Details – 1c7a01b0-f3d9-4ffb-9530-93fe5d2e6f97

Great job, no security vulnerabilities found in this Pull Request

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 6 lines in your changes missing coverage. Please review.

Project coverage is 48.06%. Comparing base (37cdefb) to head (7bd230a).
Report is 17 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Api/Vault/Controllers/CiphersController.cs	25.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6061      +/-   ##
==========================================
- Coverage   51.35%   48.06%   -3.29%     
==========================================
  Files        1703     1730      +27     
  Lines       75567    76305     +738     
  Branches     6799     6844      +45     
==========================================
- Hits        38805    36678    -2127     
- Misses      35234    38138    +2904     
+ Partials     1528     1489      -39     

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[gbubemismith]

Looks like the tests are failing

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud