Modernizing the DSOMM Application: Angular 13 to 21

DSOMM's Angular frontend currently runs on Angular 13, a version that reached end-of-life in 2023 and is eight major versions behind the latest release. This project migrates the application to Angular 21 through three workstreams: 1. An incremental version upgrade, 2. Adoption of Angular Signals to replace imperative state management, and 3. Packaging key views as Angular Elements for third-party embeddability. The migration follows Angular's official upgrade path, with tests and documentation updated at every step, leaving the codebase in a state that future contributors can build on rather than work around. #dsomm