feat: add VisynEvents to send global events, incl. better Sentry integration

[puehringer]

Developer Checklist (Definition of Done)

Issue

• All acceptance criteria from the issue are met
• Tested in latest Chrome/Firefox

UI/UX/Vis

• Requires UI/UX/Vis review
  • Reviewer(s) are notified (tag assignees)
  • Review has occurred (link to notes)
  • Feedback is included in this PR
  • Reviewer(s) approve of concept and design

Code

• Branch is up-to-date with the branch to be merged with, i.e., develop
• Code is cleaned up and formatted
• Unit tests are written (frontend/backend if applicable)
• Integration tests are written (if applicable)

PR

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• Add release label (e.g., release: minor) to this PR following semver
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• Summary of changes is written

Summary of changes

• Why? I was looking for a way to let apps react to the Sentry.init event (both in React but also globally). We previously had the globalEventHandler mechanism, but that is completely untyped and uses a custom event system (inspired by jQuery). The modern way to do this is via window.dispatchEvent, and the VisynEvent is just a typed wrapper around it.
• Migrates the useVisynUser, watcher, ... to the new mechanism, while keeping the old fire in place to ensure backwards compatibility. Removes usage of session storage to store user, as that is not recommended and has been replaced in favor of a "memory" store, i.e. a variable
• Exposes hooks useVisynEventCallback and useVisynEventValue to listen to the changes/values of the events.
• Adds a main_app entrypoint to the server to finally give us a way of what the primary plugin is. With that, we can send proper Sentry release information.

Screenshots

Additional notes for the reviewer(s)

Thanks for creating this pull request 🤗

PR Overview

This PR introduces a typed event mechanism ("VisynEvents") to replace and augment the legacy global event handling for key application events such as Sentry initialization and user session changes. Key changes include:

• Adding new hooks (useVisynEventCallback and useVisynEventValue) to listen to typed events.
• Defining the VisynEventMap and supporting functions (dispatchVisynEvent, addVisynEventListener, removeVisynEventListener) for global event dispatching.
• Migrating existing event usage (in UserSession, SessionWatcher, VisynAppProvider, etc.) from the legacy globalEventHandler mechanism to the new VisynEvents system.

Reviewed Changes

File	Description
src/hooks/useVisynEventValue.tsx	New hook to subscribe to event values via the new mechanism.
src/hooks/useVisynEventCallback.tsx	New hook to listen for event triggers using a stable callback.
src/app/VisynEvents.ts	Defines the typed event interface and helper functions.
src/demo/index.initialize.tsx	Demonstrates usage of sending and listening to a sentryInitialized event.
src/security/UserSession.ts	Migrates user login/logout events to use dispatchVisynEvent.
src/hooks/useVisynUser.ts	Simplifies user retrieval by leveraging the updated VisynAppContext.
src/base/event.ts	Marks legacy event handling APIs as deprecated.
src/app/VisynAppProvider.ts	Updates Sentry initialization and user session propagation to use new events.
src/security/watcher.ts	Adjusts session watcher to listen to new user events.
src/demo/MainApp.tsx	Switches from the old context hook to the new useVisynUser hook.

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