Resolve 15 tracked TODO comments

[david-acm]

Problem

There are at least 15 TODO comments scattered across the codebase marking unfinished work. They represent deferred decisions that accumulate technical debt and confuse future readers.

Inventory

File	Line	TODO text
src/Farkle/Domain/GameAggregate/Game.cs	104	(raw exception throw — replace with Result)
src/Farkle/Domain/GameAggregate/GameState.cs	21	TODO: Remove nullable (for GameId?)
src/Farkle/Endpoints/StartGameEndpoint.cs	31	(player/game wiring incomplete)
src/Farkle/Endpoints/JoinPlayerEndpoint.cs	21	(missing validation)
src/Farkle/Endpoints/KeepDiceEndpoint.cs	25	(missing validation)
src/Farkle/GameService.cs	41	(incomplete implementation)
src/Farkle/GameService.cs	48	(incomplete implementation)
src/Farkle/FarkleModuleServiceExtensions.cs	28	(config binding incomplete)
src/Farkle/FarkleModuleServiceExtensions.cs	29	(config binding incomplete)
src/WebApp.Client/Pages/Game/Game.razor.cs	11	(component wiring)
src/WebApp.Client/Features/Actions/JoinPlayer.cs	11	(player name not captured)
src/WebApp.Client/Features/Actions/JoinPlayer.cs	20	(empty player name sent)
src/WebApp.Client/Features/Actions/JoinPlayer.cs	23	(state update missing)
tests/Farkle.WebTests/GameApiWebAppFactory.cs	31	(container config incomplete)
tests/Farkle.WebTests/GameApiWebAppFactory.cs	32	(container config incomplete)

Approach

Work through each TODO and either:

1. Implement the missing logic (preferred), or
2. Delete the comment if the concern is no longer valid, or
3. Convert to a new GitHub issue if it's a sizeable feature (link back here)

Related issues: #31 (Ardalis.Result), #32 (nullable GameId), #8 (player name input)

Acceptance Criteria

• Zero TODO comments remain in the production source tree after the PR
• Each addressed item has a commit message or inline note explaining the resolution
• dotnet build produces 0 warnings related to these files