Replace ngOnInit by appropriate signal handling

[dbeuchler]

for #1061

Migrated all BehaviorSubject, Subject, and ReplaySubject patterns to Angular signals to replace ngOnInit by appropriate signal handling with effect. Replaced Observable-based patterns (toSignal, .subscribe()) with direct signal references, computed(), and effect().

• Replaced all .update(_ => value) calls (where the previous value is unused) with .set(value)
• Standardized all effect() and untracked() calls to multi-line block.
• Removed ngOnInit, ngOnDestroy, OnInit, OnDestroy, and Subscription where effects or signals made them unnecessary.