core/cli: Click slash registry with awaitlet bridge

Register REPL slash commands as a Click Group (params, UsageError, help).
Dispatch via awaitlet.async_def so sync command bodies can awaitlet()
async memory/confirm work. Completer and /help derive from the registry.

pyproject.toml

@@ -13,7 +13,8 @@ dependencies = [
   "tomlkit>=0.15.0",
   "sqlalchemy>=2.0.51",
   "aiosqlite>=0.22.1",
-  "click>=8.4.2"
+  "click>=8.4.2",
+  "awaitlet>=0.0.1"
 ]
 requires-python = ">=3.14,<4"
 readme = "README.md"