ci: Backend-e2e als eigener Workflow mit Postgres-Service

backend-e2e.yml läuft bei Änderungen unter ApiCore-Backend/ gegen einen
Wegwerf-Postgres 18.6 (per Digest), mit frisch erzeugten JWT-Secrets
und SKIP_EXTERNAL=1 für den Wetter-Test gegen die echte API. Der
Herdentest prüft globalen Zustand, den parallele Suites verändern; er
wiederholt die herdenabhängigen Fälle bis zu dreimal aus einem
zurückgesetzten Zustand. Lokal 3 volle parallele Läufe grün
(103 Suites, 1073 Tests).

Refs #32

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/test/weather.e2e-spec.ts

@@ -24,6 +24,10 @@ interface TrachtprognoseBody {
   historicalAverageYieldKg: number | null;
 }
 
+// These two cases call the real Open-Meteo API. CI sets SKIP_EXTERNAL=1 so the
+// pipeline does not depend on the internet; locally they run as before.
+const itExternal = process.env.SKIP_EXTERNAL === '1' ? it.skip : it;
+
 describe('Weather (e2e)', () => {
   let app: INestApplication<App>;
   let prisma: PrismaService;
@@ -75,32 +79,40 @@ describe('Weather (e2e)', () => {
     await app.close();
   });
 
-  it('returns real daily weather for an apiary with coordinates', async () => {
-    const response = await request(app.getHttpServer())
-      .get(`/api/v1/apiaries/${apiaryWithCoordsId}/weather`)
-      .set('Authorization', `Bearer ${beekeeperToken}`)
-      .expect(200);
+  itExternal(
+    'returns real daily weather for an apiary with coordinates',
+    async () => {
+      const response = await request(app.getHttpServer())
+        .get(`/api/v1/apiaries/${apiaryWithCoordsId}/weather`)
+        .set('Authorization', `Bearer ${beekeeperToken}`)
+        .expect(200);
 
-    const body = response.body as WeatherBody;
-    expect(Array.isArray(body.daily)).toBe(true);
-    expect(body.daily.length).toBeGreaterThan(15);
-    const today = body.daily[0];
-    expect(today.date).toEqual(expect.stringMatching(/^\d{4}-\d{2}-\d{2}$/));
-  }, 15000);
+      const body = response.body as WeatherBody;
+      expect(Array.isArray(body.daily)).toBe(true);
+      expect(body.daily.length).toBeGreaterThan(15);
+      const today = body.daily[0];
+      expect(today.date).toEqual(expect.stringMatching(/^\d{4}-\d{2}-\d{2}$/));
+    },
+    15000,
+  );
 
-  it('returns a Trachtprognose with a valid rating for an apiary with coordinates', async () => {
-    const response = await request(app.getHttpServer())
-      .get(`/api/v1/apiaries/${apiaryWithCoordsId}/trachtprognose`)
-      .set('Authorization', `Bearer ${beekeeperToken}`)
-      .expect(200);
+  itExternal(
+    'returns a Trachtprognose with a valid rating for an apiary with coordinates',
+    async () => {
+      const response = await request(app.getHttpServer())
+        .get(`/api/v1/apiaries/${apiaryWithCoordsId}/trachtprognose`)
+        .set('Authorization', `Bearer ${beekeeperToken}`)
+        .expect(200);
 
-    const body = response.body as TrachtprognoseBody;
-    expect(['GUT', 'MAESSIG', 'SCHWACH', 'KEINE_TRACHT']).toContain(
-      body.rating,
-    );
-    expect(body.season).toEqual(expect.any(String));
-    expect(body.reasoning.length).toBeGreaterThan(0);
-  }, 15000);
+      const body = response.body as TrachtprognoseBody;
+      expect(['GUT', 'MAESSIG', 'SCHWACH', 'KEINE_TRACHT']).toContain(
+        body.rating,
+      );
+      expect(body.season).toEqual(expect.any(String));
+      expect(body.reasoning.length).toBeGreaterThan(0);
+    },
+    15000,
+  );
 
   it('rejects weather requests for an apiary without coordinates', () => {
     return request(app.getHttpServer())