fix(mobile): share() is fire-and-forget, so four of its native outcomes can never reach the page

The injected bridge sends share with no callbackId and returns nothing:

// packages/ios/templates/CraftApp.swift:2010
share: function(text) {
    window.webkit.messageHandlers.craft.postMessage({action: 'share', text: text});
},

// packages/android/templates/CraftBridge.kt.template
share: function(text, title) {
    CraftAndroid.share(text, title || '');
},

The iOS native side, meanwhile, is written as though a promise were waiting (CraftApp.swift:666-677):

case "share":
    if config.enableShare {
        if let options = body["options"] as? [String: Any] {
            share(options: options, callbackId: callbackId)
        } else if let text = body["text"] as? String {
            share(options: ["text": text], callbackId: callbackId)
        } else {
            rejectCallback(callbackId, error: "Nothing to share", code: "INVALID_ARGUMENT")
        }
    } else {
        rejectCallback(callbackId, error: "Sharing is disabled", code: "CAPABILITY_DISABLED")
    }

callbackId is always nil here, and both resolveCallback and rejectCallback open with guard let id = callbackId else { return }. So all four outcomes — shared, cancelled, nothing-to-share, capability-disabled — are silently discarded.

The visible consequence is that window.craft.share('x') in an app with enableShare: false does nothing at all and reports nothing. Observed on a simulator while building #199: the call appeared to succeed because it returned undefined, which Promise.resolve turns into a resolved promise.

Every other capability-gated action on this surface returns a promise and rejects with CAPABILITY_DISABLED; share is the odd one out. Making it return a promise and pass a callbackId would need no change to the Swift side, which is already written for it.

Not covered by the mobile E2E suite for the same reason it is a bug: there is nothing to assert on.