feat(cli): add agent-ready C# command-line client

[gustmrg]

Summary

• add the independently versioned bitfinance-cli C# project with JSON-first output and documented exit codes
• expose organization, dashboard, bill, expense, mutation, and document commands with mandatory organization IDs
• add main-branch validation and version-gated Linux x64/ARM64 GitHub Release binaries
• document installation, configuration, commands, and release procedures

Validation

• dotnet build apps/cli/src/BitFinance.Cli.csproj -c Release
• dotnet test apps/cli/tests/BitFinance.Cli.UnitTests/BitFinance.Cli.UnitTests.csproj -c Release (49 passed)
• dotnet format --verify-no-changes for source and tests
• workflow YAML and shell syntax validation
• Linux x64 executable smoke test and x64/ARM64 package validation