Switch whiteboard note storage from legacy DB rows to per-note JSON files and add migration support. Update WhiteboardNoteSnapshot schema (version bump, viewport, canvas, expires, PathSvgData) and change IWhiteboardNotePersistenceService.SaveNote to return bool to surface write failures (e.g. read-only files). Implement file-based WhiteboardNotePersistenceService with legacy DB migration/cleanup, retention handling, and logging. Add comprehensive unit tests for persistence, stroke path builder, SVG import and viewport helper. Also add ThirdParty/DotNetCampus.InkCanvas project and reference it in the main csproj, and bump PostHog package to 2.6.0.
Introduce a new LanMountainDesktop.Shared.IPC project implementing a public IPC host and client (LanMountainDesktopIpcClient, PublicIpcHostService), IPC constants and routed notify IDs, DTOs and DI helpers for registering public services. Update Plugin SDK to allow plugins to contribute public IPC services and registrations, add related descriptors/records and extension helpers. Migrate Launcher/App to use the new public IPC for startup/loading notifications and wiring (including TryConnect helper), switch LoadingStateReporter to use the external notification publisher, and add host-side public services (app info, shell control, plugin catalog). Include integration tests and spec/checklist/docs for the external IPC public API.
