[PM-40640] Adjust error messages for Send policy enforcement

[mcamirault]

🎟️ Tracking

https://bitwarden.atlassian.net/browse/PM-40640

📔 Objective

This PR adjusts the error strings that are returned when Send policies are enforced so that all instances of "Enterprise Policy" are corrected to "Enterprise policy". No logic changes, only error messages.

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

This PR changes "Enterprise Policy" to "Enterprise policy" in five BadRequestException messages in SendValidationService.ValidateUserCanSaveAsync and updates the matching assertions in SendValidationServiceTests and NonAnonymousSendCommandTests. No control flow, validation logic, or public contracts were altered. All Send policy messages in the file now use consistent casing, matching the already-lowercase messages for allowed Send types and deletion dates, and every test asserting on these strings was updated in step.

Code Review Details

No findings.

Notes considered and not raised as findings:

• src/Core/Vault/Services/Implementations/CipherService.cs:151 and the PolicyRequirements/README.md examples still use "Enterprise Policy", but those are outside the Send policy scope stated in the PR objective.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.64%. Comparing base (8414547) to head (32abf39).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8196   +/-   ##
=======================================
  Coverage   63.64%   63.64%           
=======================================
  Files        2373     2373           
  Lines      102846   102846           
  Branches     9328     9328           
=======================================
  Hits        65456    65456           
  Misses      35161    35161           
  Partials     2229     2229           

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