fix(ui): prioritize exact Nexus search matches

[ModifAmorphic]

Summary

• use Nexus relevance ordering so older exact-title mods are not excluded by capped newest-first results
• rank normalized exact matches ahead of non-exact candidates for automatic and manual load-order searches while preserving the existing selection safeguards
• add Scoreboard mod 22 regression coverage and update the Nexus and UI references

Validation

• dotnet build src/modificus-curator.sln --configuration Release
• dotnet test src/modificus-curator.sln --configuration Release (2,474 passed)
• dotnet format src/modificus-curator.sln --verify-no-changes
• independent code review approved and QA passed