Create ui-watchtower framework-agnostic core engine package #35

Extract the framework-agnostic engine logic into a standalone ui-watchtower package, with ngx-ui-watchtower serving as a thin Angular adapter. This separation will allow additional adapters for other frameworks or libraries to be introduced in the future.

Plan

The work is delivered as a stack of eight pull requests, each tracked by a sub-issue, merged bottom first:

• Add API, type and wire-protocol safety nets for the Angular package #37 Add API, type and wire-protocol safety nets for the Angular package
• Scaffold the ui-watchtower core package #38 Scaffold the ui-watchtower core package
• Move models, redaction and scenarios into the core #39 Move models, redaction and scenarios into the core
• Add the framework-independent telemetry engine #40 Add the framework-independent telemetry engine
• Move the shell/fragment broadcast protocol into the core #41 Move the shell/fragment broadcast protocol into the core
• Move the AWS RUM sink into the core's rum entry point #42 Move the AWS RUM sink into the core's rum entry point
• Smoke-test the packed packages in real consumers #43 Smoke-test the packed packages in real consumers
• Release and publish both packages independently, with docs #44 Release and publish both packages independently, with docs