feat: add build-aware compose stack updates (#1561)

Detect services with build: in the update preview and run compose build --pull
plus pull --ignore-buildable when Update is triggered on those stacks, while
keeping the existing pull-only path for image-only stacks.

backend/src/__tests__/compose-build-services.test.ts

@@ -0,0 +1,64 @@
+import { describe, it, expect } from 'vitest';
+import {
+    extractBuildServicesFromCompose,
+    extractBuildServicesFromRenderedConfig,
+} from '../services/ImageUpdateService';
+
+describe('extractBuildServicesFromCompose', () => {
+    it('returns service names that declare build', () => {
+        const yaml = `
+services:
+  web:
+    build: .
+  api:
+    image: nginx:1.25
+  worker:
+    build:
+      context: ./worker
+      dockerfile: Dockerfile
+`;
+        expect(extractBuildServicesFromCompose(yaml).sort()).toEqual(['web', 'worker']);
+    });
+
+    it('returns empty for image-only stacks', () => {
+        const yaml = `
+services:
+  web:
+    image: nginx:1.25
+`;
+        expect(extractBuildServicesFromCompose(yaml)).toEqual([]);
+    });
+
+    it('ignores empty build sections', () => {
+        const yaml = `
+services:
+  web:
+    build: ""
+  api:
+    build: {}
+`;
+        expect(extractBuildServicesFromCompose(yaml)).toEqual([]);
+    });
+});
+
+describe('extractBuildServicesFromRenderedConfig', () => {
+    it('reads build services from a rendered compose json model', () => {
+        const rendered = JSON.stringify({
+            services: {
+                app: { build: { context: '/app' }, image: 'myapp:latest' },
+                cache: { image: 'redis:7' },
+            },
+        });
+        expect(extractBuildServicesFromRenderedConfig(rendered)).toEqual(['app']);
+    });
+
+    it('includes override-only build services from merged model', () => {
+        const rendered = JSON.stringify({
+            services: {
+                web: { image: 'nginx:1.25' },
+                sidecar: { build: './sidecar' },
+            },
+        });
+        expect(extractBuildServicesFromRenderedConfig(rendered)).toEqual(['sidecar']);
+    });
+});