Angular 19 - Introduction to linkedSignal

Angular 19 introduces `linkedSignal`, a new reactive primitive that creates writable signals automatically synchronized with a source signal. Unlike `computed()` signals which are read-only, `linkedSignal` allows explicit value setting while still reacting to upstream changes. Two usage patterns are covered: a full object syntax with `source` and `computation` properties, and a shorthand function syntax. A practical example shows resetting a student count whenever a course ID input changes, demonstrating how `linkedSignal` simplifies reset patterns and improves flexibility over traditional computed signals.