[Add] create and delete a ParameterSubscription from the Model Editor; fixes #779

[samatstariongroup]

Prerequisites

• I have written a descriptive pull-request title
• I have verified that there are no overlapping pull-requests open
• I have verified that I am following the COMET-WEB code style guidelines
• I have provided test coverage for my change (where applicable)

Description

• New subscribe button on each parameter card in the Model Editor whose owner is a different DomainOfExpertise than the current one; opens a confirm popup and creates a ParameterSubscription (with one ParameterSubscriptionValueSet per source ParameterValueSet) for the current domain.
• New unsubscribe button on cards where the current domain already has a subscription; opens a confirm popup and deletes only the ParameterSubscription — the parent Parameter is preserved.
• Card refresh after either action relies on the existing OnEndUpdate → OnSessionRefreshed → SelectElement message-bus chain (no manual row mutation), so the card automatically rebuilds with the post-server state — including subscription-aware ActualValue from the matching ParameterSubscriptionValueSet.

layout is sub-optimal, we'll redesign the page in a separate issue and PR