fix(frontend): detruit les graphiques avec leur composant

Chart.js conserve chaque instance dans un registre lie au canvas et lui
attache un observateur de redimensionnement. Sans destroy, tout survit a la
destruction du composant, et une re-creation sur le meme canvas echoue avec
"Canvas is already in use".

Les doubles de test gagnent destroy : TestBed detruit les fixtures apres
chaque test, un mock sans cette methode fait tomber les specs existantes.

apps/frontend/src/app/shared/components/consumption-gauge/consumption-gauge.spec.ts

@@ -1,16 +1,28 @@
 import { TestBed } from '@angular/core/testing';
 import { vi } from 'vitest';
+import { Chart } from 'chart.js';
 import { ConsumptionGauge } from './consumption-gauge';
 
 vi.mock('chart.js', () => {
   class ChartMock {
-    update = vi.fn();
-    data = { datasets: [{}] };
+    static instances: ChartMock[] = [];
     static register = vi.fn();
+    update = vi.fn();
+    destroy = vi.fn();
+    data = { datasets: [{}] };
+    constructor() {
+      ChartMock.instances.push(this);
+    }
   }
   return { Chart: ChartMock, registerables: [] };
 });
 
+type ChartDouble = { destroy: ReturnType<typeof vi.fn> };
+
+function lastChart(): ChartDouble | undefined {
+  return (Chart as unknown as { instances: ChartDouble[] }).instances.at(-1);
+}
+
 describe('ConsumptionGauge', () => {
   it('se crée sans erreur avec des entrées valides', () => {
     TestBed.configureTestingModule({ imports: [ConsumptionGauge] });
@@ -31,4 +43,17 @@ describe('ConsumptionGauge', () => {
 
   expect(() => fixture.detectChanges()).not.toThrow();
 });
+
+  it('détruit le graphique quand le composant est détruit', () => {
+    TestBed.configureTestingModule({ imports: [ConsumptionGauge] });
+    const fixture = TestBed.createComponent(ConsumptionGauge);
+    fixture.componentRef.setInput('consumption', 300);
+    fixture.componentRef.setInput('capacity', 1000);
+    fixture.detectChanges();
+
+    const chart = lastChart();
+    fixture.destroy();
+
+    expect(chart?.destroy).toHaveBeenCalledTimes(1);
+  });
 });

apps/frontend/src/app/shared/components/consumption-gauge/consumption-gauge.ts

@@ -1,4 +1,12 @@
-import { Component, ElementRef, ViewChild, input, effect, AfterViewInit } from '@angular/core';
+import {
+  Component,
+  ElementRef,
+  ViewChild,
+  input,
+  effect,
+  AfterViewInit,
+  OnDestroy,
+} from '@angular/core';
 import { Chart, registerables } from 'chart.js';
 
 Chart.register(...registerables);
@@ -9,7 +17,7 @@ Chart.register(...registerables);
   templateUrl: './consumption-gauge.html',
   styleUrl: './consumption-gauge.scss',
 })
-export class ConsumptionGauge implements AfterViewInit {
+export class ConsumptionGauge implements AfterViewInit, OnDestroy {
   consumption = input.required<number>();
   capacity = input.required<number>();
 
@@ -52,4 +60,8 @@ export class ConsumptionGauge implements AfterViewInit {
       },
     });
   }
+
+  ngOnDestroy(): void {
+    this.chart?.destroy();
+  }
 }

apps/frontend/src/app/shared/components/site-load-chart/site-load-chart.spec.ts

@@ -1,16 +1,28 @@
 import { TestBed } from '@angular/core/testing';
 import { vi } from 'vitest';
+import { Chart } from 'chart.js';
 import { SiteLoadChart } from './site-load-chart';
 
 vi.mock('chart.js', () => {
   class ChartMock {
-    update = vi.fn();
-    data = { datasets: [{}] };
+    static instances: ChartMock[] = [];
     static register = vi.fn();
+    update = vi.fn();
+    destroy = vi.fn();
+    data = { datasets: [{}] };
+    constructor() {
+      ChartMock.instances.push(this);
+    }
   }
   return { Chart: ChartMock, registerables: [] };
 });
 
+type ChartDouble = { destroy: ReturnType<typeof vi.fn> };
+
+function lastChart(): ChartDouble | undefined {
+  return (Chart as unknown as { instances: ChartDouble[] }).instances.at(-1);
+}
+
 describe('SiteLoadChart', () => {
   it('se crée sans erreur avec une liste de sites valide', () => {
     TestBed.configureTestingModule({ imports: [SiteLoadChart] });
@@ -35,4 +47,25 @@ describe('SiteLoadChart', () => {
 
   expect(() => fixture.detectChanges()).not.toThrow();
 });
+
+  it('détruit le graphique quand le composant est détruit', () => {
+    TestBed.configureTestingModule({ imports: [SiteLoadChart] });
+    const fixture = TestBed.createComponent(SiteLoadChart);
+    fixture.componentRef.setInput('sites', [
+      {
+        site_id: 'S1',
+        site_name: 'A',
+        current_consumption_kw: 50,
+        capacity_kw: 100,
+        load_percent: 50,
+        data_quality: 'good',
+      },
+    ]);
+    fixture.detectChanges();
+
+    const chart = lastChart();
+    fixture.destroy();
+
+    expect(chart?.destroy).toHaveBeenCalledTimes(1);
+  });
 });

apps/frontend/src/app/shared/components/site-load-chart/site-load-chart.ts

@@ -1,4 +1,12 @@
-import { Component, ElementRef, ViewChild, input, effect, AfterViewInit } from '@angular/core';
+import {
+  Component,
+  ElementRef,
+  ViewChild,
+  input,
+  effect,
+  AfterViewInit,
+  OnDestroy,
+} from '@angular/core';
 import { Chart, registerables } from 'chart.js';
 import { SiteSummary } from '../../models/stats.model';
 
@@ -17,7 +25,7 @@ const QUALITY_COLORS: Record<SiteSummary['data_quality'], string> = {
   templateUrl: './site-load-chart.html',
   styleUrl: './site-load-chart.scss',
 })
-export class SiteLoadChart implements AfterViewInit {
+export class SiteLoadChart implements AfterViewInit, OnDestroy {
   sites = input.required<SiteSummary[]>();
 
   @ViewChild('canvas') private canvasRef!: ElementRef<HTMLCanvasElement>;
@@ -59,4 +67,8 @@ export class SiteLoadChart implements AfterViewInit {
       },
     });
   }
+
+  ngOnDestroy(): void {
+    this.chart?.destroy();
+  }
 }