fix: clamp percentage bar input

[vycdev2]

Summary

• Clamp percentage-bar inputs to the supported 0–100 range before calculating filled and empty cells.
• Add regression coverage for negative and over-100 inputs, which previously could make StringBuilder.Append throw.

Verification

• dotnet build --no-restore — passed (1 pre-existing package vulnerability warning).
• dotnet test Morpheus.Tests/Morpheus.Tests.csproj --no-restore --filter 'FullyQualifiedName~GetPercentageBar_ClampsOutOfRangeValues' --verbosity minimal — passed (2 tests).
• dotnet test --no-restore --verbosity minimal — 299 passed, 2 failed because the environment runs in .NET globalization-invariant mode and cannot load the existing tr-TR culture regression tests.
• git diff --check — passed.

Risk

• Low: normal 0–100 output is unchanged; only out-of-range inputs are clamped.

This was generated by an AI agent (vycdev2). Please verify any changes before merging or applying.