feat(combat): rejoin the running combat instead of dead-ending

Attacking while a combat is already active returned COMBAT_ALREADY_ACTIVE
and left the hunt page showing an error the player could not act on, with
no way back into the fight they were already in.

Add GET /api/combats/active so the client can resolve that combat, and
have the hunt page navigate into it when an attack is rejected for this
reason. CombatStore now also exposes the error code so callers can tell
this case apart from a genuinely failed attack.

apps/web/src/app/features/hunting/hunt-page/hunt-page.component.spec.ts

@@ -98,7 +98,9 @@ describe('HuntPageComponent', () => {
   let combatStore: {
     combat: ReturnType<typeof signal<Combat | null>>;
     error: ReturnType<typeof signal<string | null>>;
+    errorCode: ReturnType<typeof signal<string | null>>;
     startCombat: ReturnType<typeof vi.fn>;
+    loadActiveCombat: ReturnType<typeof vi.fn>;
     clearError: ReturnType<typeof vi.fn>;
   };
   let router: Router;
@@ -118,7 +120,9 @@ describe('HuntPageComponent', () => {
     combatStore = {
       combat: signal<Combat | null>(null),
       error: signal<string | null>(null),
+      errorCode: signal<string | null>(null),
       startCombat: vi.fn(() => Promise.resolve()),
+      loadActiveCombat: vi.fn(() => Promise.resolve(null)),
       clearError: vi.fn(),
     };
 
@@ -226,6 +230,47 @@ describe('HuntPageComponent', () => {
     expect(router.navigate).not.toHaveBeenCalledWith(['/combat', expect.anything()]);
   });
 
+  it('rejoins the running combat when the attack is rejected with COMBAT_ALREADY_ACTIVE', async () => {
+    const fixture = await setup(burnedRoad, threeEncounterHunt);
+    combatStore.startCombat.mockImplementation(async () => {
+      combatStore.errorCode.set('COMBAT_ALREADY_ACTIVE');
+      combatStore.error.set('Du befindest dich bereits in einem Kampf.');
+    });
+    combatStore.loadActiveCombat.mockResolvedValue({ ...startedCombat, id: 'combat-running' });
+    const element = fixture.nativeElement as HTMLElement;
+
+    const attackButtons = Array.from(element.querySelectorAll('button')).filter(
+      (button) => button.textContent?.trim() === 'Angreifen',
+    );
+    attackButtons[0].click();
+    await Promise.resolve();
+    await Promise.resolve();
+    await Promise.resolve();
+
+    expect(combatStore.loadActiveCombat).toHaveBeenCalledOnce();
+    expect(router.navigate).toHaveBeenCalledWith(['/combat', 'combat-running']);
+  });
+
+  it('does not look for a running combat when the attack fails for another reason', async () => {
+    const fixture = await setup(burnedRoad, threeEncounterHunt);
+    combatStore.startCombat.mockImplementation(async () => {
+      combatStore.errorCode.set('HUNT_ENCOUNTER_ALREADY_CONSUMED');
+      combatStore.error.set('Diese Begegnung wurde bereits genutzt.');
+    });
+    const element = fixture.nativeElement as HTMLElement;
+
+    const attackButtons = Array.from(element.querySelectorAll('button')).filter(
+      (button) => button.textContent?.trim() === 'Angreifen',
+    );
+    attackButtons[0].click();
+    await Promise.resolve();
+    await Promise.resolve();
+    await Promise.resolve();
+
+    expect(combatStore.loadActiveCombat).not.toHaveBeenCalled();
+    expect(router.navigate).not.toHaveBeenCalledWith(['/combat', expect.anything()]);
+  });
+
   it('shows a combat-start error and dismisses it', async () => {
     const fixture = await setup(burnedRoad, threeEncounterHunt);
     combatStore.error.set('Du befindest dich bereits in einem Kampf.');