fix(cli): resolve lint errors and step name conflict in command bus

- Replace deprecated typing imports (Dict, Callable, Generic) with
  collections.abc.Callable and built-in dict
- Convert Command from ABC to plain base class (B024: no abstract methods)
- Convert CommandHandler to PEP 695 type parameter syntax (UP046)
- Remove unused PlanService/ProjectService imports from command_registry
- Fix ruff format: blank line before nested defs in command_registry and steps
- Rename @then('a ValueError should be raised') to domain-specific suffix
  to avoid AmbiguousStep collision with lsp_registry_steps.py

ISSUES CLOSED: #8880

features/cli_command_bus_decoupling.feature

@@ -27,7 +27,7 @@ Feature: CLI Command Bus Decoupling
   Scenario: Dispatch fails for unregistered command
     Given a command bus with no handlers
     When I dispatch a command without a registered handler
-    Then a ValueError should be raised
+    Then a ValueError should be raised for unregistered command dispatch
     And the error message should mention the command type
 
   Scenario: Handler check