[manuelmayer-dev]

Closes #1286

Summary

Plugins and built-in integrations can show toasts and dialogs on every connected Desktop and Web client through one host-owned notification service, and get the user's answer and form values back. The notification list now tracks read state, all existing host notifications go through the same manager, and there is a new action, Show Macro Deck notification.

Testing

Release build with warnings as errors, runtime, web client (including legacy), desktop UI and docs pass, as do all .NET suites except the Plugin.Cli build test, which fails locally with exit 155. Tried live with a real plugin and several clients against a running host, and manually in both UIs. Device targeting is covered by unit tests only, and the Companion is not covered. Moving existing host notifications to toasts is a follow-up (ADR 0106).

Plugin SDK / API compatibility

Additive only: a default INotificationService member on IIntegrationContext, new notifications host operations and a ui notification.result invoke, protocol major unchanged.

• No public, non-obsolete SDK or plugin protocol contract was removed or changed
• Contracts were only extended additively (new members with defaults, new optional fields, new message types)

Checklist

• Tests were added or updated where needed
• The change was verified manually where appropriate
• Documentation was updated if the change affects documented behaviour
• I reviewed and understand every submitted change