[Chore]: Migrate Program.cs to System.CommandLine 2.0.0-beta5 API

[Copilot]

This PR migrates the main application entry point in Program.cs to use System.CommandLine 2.0.0-beta5 API patterns, addressing the breaking changes introduced in the beta5 release.

Changes Made

1. Package Update

• Updated System.CommandLine from 2.0.0-beta4.22272.1 to 2.0.0-beta5.25277.114

2. Command Registration Migration

Replaced all rootCommand.AddCommand() calls with the new mutable collections pattern:

// Before (beta4)
rootCommand.AddCommand(InitProjectCommandHandler.SetupCommand(host));
rootCommand.AddCommand(DataDictionaryCommandHandler.SetupCommand(host));
// ... more commands

// After (beta5)
rootCommand.Subcommands.Add(InitProjectCommandHandler.SetupCommand(host));
rootCommand.Subcommands.Add(DataDictionaryCommandHandler.SetupCommand(host));
// ... more commands

3. Entry Point Modernization

Updated the main method to use the new parsing and invocation separation pattern:

// Before (beta4)
private static async Task Main(string[] args)
{
    // ... setup code
    await rootCommand.InvokeAsync(args);
}

// After (beta5)
private static async Task<int> Main(string[] args)
{
    // ... setup code
    var parseResult = rootCommand.Parse(args);
    return await parseResult.InvokeAsync();
}

Validation

• ✅ Created isolated test confirming API patterns work correctly
• ✅ Verified help functionality displays properly (--help)
• ✅ Confirmed error handling returns appropriate exit codes
• ✅ All 7 command registrations updated to use new syntax

Impact

• Breaking Changes: Internal only - external CLI interface remains unchanged
• Scope: Focused specifically on Program.cs entry point as requested
• Compatibility: Maintains existing command-line behavior for end users

Fixes #16.

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