fix: risolto accesso diretto ai singoli canti tramite URL e queryParams

- Aggiunto il caricamento reattivo del canto tramite un 'effect' in PlayerPage e DisplayPage.
- Ora l'applicazione attende che la lista asincrona dei canti sia popolata per caricare la canzone richiesta da URL.

src/app/pages/display/display.page.ts

@@ -1,4 +1,4 @@
-import { Component, OnInit, OnDestroy, signal, computed, inject } from '@angular/core';
+import { Component, OnInit, OnDestroy, signal, computed, effect, inject } from '@angular/core';
 import { ActivatedRoute } from '@angular/router';
 import { CantiService, Canto } from '../../services/canti.service';
 import { LyricsParserService, ParsedSection } from '../../services/lyrics-parser.service';
@@ -11,6 +11,7 @@ import { LyricsParserService, ParsedSection } from '../../services/lyrics-parser
 })
 export class DisplayPage implements OnInit, OnDestroy {
   public canto = signal<Canto | null>(null);
+  public activeSongId = signal<string | null>(null);
   public showChords = signal<boolean>(false);
   public fontSize = signal<number>(1.0);
   public currentLineIndex = signal<number>(0);
@@ -54,14 +55,24 @@ export class DisplayPage implements OnInit, OnDestroy {
   private cantiService = inject(CantiService);
   private lyricsParser = inject(LyricsParserService);
 
-  constructor() { }
+  constructor() {
+    effect(() => {
+      const id = this.activeSongId();
+      const allCanti = this.cantiService.canti();
+      if (id) {
+        const found = allCanti.find(c => c.id === id);
+        if (found) {
+          this.canto.set(found);
+        }
+      }
+    }, { allowSignalWrites: true });
+  }
 
   ngOnInit() {
     this.route.queryParams.subscribe(params => {
       const id = params['id'];
       if (id) {
-        const found = this.cantiService.getCantoById(id);
-        if (found) this.canto.set(found);
+        this.activeSongId.set(id);
       }
     });
 
@@ -70,8 +81,7 @@ export class DisplayPage implements OnInit, OnDestroy {
         this.currentLineIndex.set(event.data.index);
       }
       if (event.data.type === 'SYNC_CANTO') {
-        const found = this.cantiService.getCantoById(event.data.id);
-        if (found) this.canto.set(found);
+        this.activeSongId.set(event.data.id);
       }
       if (event.data.type === 'SYNC_CHORDS') {
         this.showChords.set(event.data.showChords);