Command built from semantic types keeps padded name/description/category, so GetCommandsByCategory misses it until a save/reload #146

What's wrong

Command has two constructors, and they normalize differently.

• The string constructor (Keybinding/Models/Command.cs ~L236-239) trims the name, description and category, and maps a blank description or category to null.
• The semantic constructor (CommandId, CommandName, CommandDescription?, CommandCategory?) (~L196-214) trims only the id, which was the A Command built from a CommandId with surrounding whitespace registers but can never be found, bound or unregistered #123 fix. The name, description and category are stored exactly as given.

CommandRegistry.GetCommandsByCategory (Services/CommandRegistry.cs ~L60-62) trims its input and compares with OrdinalIgnoreCase, so a stored category with padding never matches.

Reproduction (verified)

var cmd = new Command(
    CommandId.Create("edit.copy"),
    CommandName.Create(" Copy "),
    CommandDescription.Create("   "),
    CommandCategory.Create("Editing "));
// Stored: Name=" Copy ", Description="   ", Category="Editing "
registry.RegisterCommand(cmd);
registry.GetCommandsByCategory("Editing");   // 0 results
registry.GetCommandsByCategory("Editing ");  // 0 results (the input is trimmed)

After SaveAsync() and a reload, the command is rebuilt through the string constructor and trimmed, and it then appears under "Editing". The same command behaves differently before and after a round-trip.

Suggested fix / acceptance criteria

• Have the semantic constructor apply the same normalization as the string constructor: trim the name, description and category, and turn a blank description or category into null. Ideally both constructors share one helper.
• Add tests alongside CommandIdWhitespaceTests: padded name and category are trimmed, a whitespace-only description or category becomes null, and GetCommandsByCategory("Editing") finds the command without a save and reload.