feat: convert soft_limit to limit (#22048)

In relation to
[`internal#1281`](https://github.com/coder/internal/issues/1281)

Remove the `soft_limit` field from the `Feature` type and simplify
license limit handling. This change:

- Removes the `soft_limit` field from the API and SDK
- Uses the soft limit value as the single `limit` value in the UI and
API
- Simplifies warning logic to only show warnings when the limit is
exceeded
- Updates tests to reflect the new behavior
- Updates the UI to use the single limit value for display

enterprise/coderd/workspaces_test.go

@@ -4728,7 +4728,7 @@ func TestWorkspaceAITask(t *testing.T) {
 			Features: license.Features{
 				codersdk.FeatureTemplateRBAC: 1,
 			},
-		}).ManagedAgentLimit(10, 20),
+		}).ManagedAgentLimit(10),
 	})
 
 	client, _ := coderdtest.CreateAnotherUser(t, owner, first.OrganizationID,