KeybindingManager ignores a registered IKeybindingService: it always news up its own KeybindingService, so a custom or decorated service never takes effect #208

Plan reference

ARCHITECTURE_ANALYSIS.md L20-26 and L62-66 (status: draft):

• Service Interfaces: All core services are interface-based, allowing custom implementations
• Dependency Injection: All dependencies are injected via constructor

What exists today

• IKeybindingService is registered in DI (Keybinding/Extensions/ServiceCollectionExtensions.cs:45, 92).
• KeybindingManager exposes IKeybindingService Keybindings (Keybinding/KeybindingManager.cs:73).

What's missing

The manager's constructor hard-codes the implementation:

// Keybinding/KeybindingManager.cs:57
Keybindings = new KeybindingService(Commands, Profiles);

Neither constructor accepts an IKeybindingService. So an app that registers a decorator never gets it from the manager, for example a decorator that logs or audits rebinds, or one that enforces app-specific conflict rules. The DI container then holds two different keybinding services.

Reproduction (HEAD b035bdb)

var s = new ServiceCollection();
s.AddSingleton<IKeybindingService>(sp => new LoggingService(new KeybindingService(
    sp.GetRequiredService<ICommandRegistry>(), sp.GetRequiredService<IProfileManager>())));
s.AddKeybinding(tmpDir);
using var sp = s.BuildServiceProvider();
var registered = sp.GetRequiredService<IKeybindingService>();
var m = sp.GetRequiredService<KeybindingManager>();
Console.WriteLine($"registered: {registered.GetType().Name}; manager.Keybindings: {m.Keybindings.GetType().Name}; same instance: {ReferenceEquals(registered, m.Keybindings)}");
// registered: LoggingService; manager.Keybindings: KeybindingService; same instance: False

LoggingService is a pass-through decorator.

Acceptance criteria

• Add a constructor that takes IKeybindingService alongside the existing three dependencies, and make it the one DI selects.
• Keep the 3-argument constructor for standalone use. It goes on creating a KeybindingService.
• KeybindingManagerFactory.CreateManager() passes the registered IKeybindingService.
• Add a test asserting that manager.Keybindings is the instance registered in DI.

Dependencies

None. Related, but separate: #145 covers IKeybindingConfiguration not being read.