fix(dashboard): defensive null guard in ContributorStack; fix spec makeDoc factories

frontend/src/lib/components/ContributorStack.svelte

@@ -9,16 +9,18 @@ interface Props {
 }
 
 let { contributors, hasMore }: Props = $props();
+
+const safeContributors = $derived(contributors ?? []);
 </script>
 
-{#if contributors.length === 0}
+{#if safeContributors.length === 0}
 	<span
 		class="inline-block h-[22px] w-[22px] flex-shrink-0 rounded-full border-[1.5px] border-dashed border-[#cdcbbf]"
 		title="Noch niemand angefangen"
 	></span>
 {:else}
 	<span class="inline-flex items-center">
-		{#each contributors as actor, i (actor.name ?? actor.initials + i)}
+		{#each safeContributors as actor, i (actor.name ?? actor.initials + i)}
 			<span
 				class="inline-flex h-[22px] w-[22px] flex-shrink-0 items-center justify-center rounded-full font-sans text-[9px] font-bold text-white ring-2 ring-white {i > 0 ? '-ml-1.5' : ''}"
 				style="background-color: {actor.color || '#8c9aa3'};"

frontend/src/lib/components/MissionControlStrip.svelte.spec.ts

@@ -20,6 +20,8 @@ function makeDoc(
 		annotationCount: 0,
 		textedBlockCount: 0,
 		reviewedBlockCount: 0,
+		contributors: [],
+		hasMoreContributors: false,
 		...overrides
 	};
 }

frontend/src/lib/components/ReadyColumn.svelte.spec.ts

@@ -15,6 +15,8 @@ function makeDoc(overrides: Partial<TranscriptionQueueItemDTO> = {}): Transcript
 		annotationCount: 0,
 		textedBlockCount: 0,
 		reviewedBlockCount: 0,
+		contributors: [],
+		hasMoreContributors: false,
 		...overrides
 	};
 }

frontend/src/lib/components/SegmentationColumn.svelte.spec.ts

@@ -15,6 +15,8 @@ function makeDoc(overrides: Partial<TranscriptionQueueItemDTO> = {}): Transcript
 		annotationCount: 0,
 		textedBlockCount: 0,
 		reviewedBlockCount: 0,
+		contributors: [],
+		hasMoreContributors: false,
 		...overrides
 	};
 }

frontend/src/lib/components/TranscriptionColumn.svelte.spec.ts

@@ -15,6 +15,8 @@ function makeDoc(overrides: Partial<TranscriptionQueueItemDTO> = {}): Transcript
 		annotationCount: 0,
 		textedBlockCount: 0,
 		reviewedBlockCount: 0,
+		contributors: [],
+		hasMoreContributors: false,
 		...overrides
 	};
 }