fix: bound stock portfolio embeds

[vycdev2]

Summary

• keep large stock portfolios within Discord’s embed description limit
• preserve full portfolio totals while clearly reporting omitted holding rows
• add a command-path regression test for a 50-holding portfolio

Verification

• dotnet test Morpheus.Tests/Morpheus.Tests.csproj --filter FullyQualifiedName~StocksModuleTests.StockPortfolioAsync_BoundsLargePortfolioDescription — passed (1 test)
• dotnet build — passed with 0 warnings and 0 errors
• dotnet test --no-build — passed (620 passed, 3 skipped)
• python3 -m unittest tools.test_generate_commands_md — passed (3 tests)
• git diff --check — passed

Risk

• Low. The change only bounds portfolio rendering; balances and aggregate totals still include every holding.

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