fix(ui): use De Gruyter long arrows for swap button and timeline entries

Swap button: stack right/left arrows vertically at h-3.5 for a
compact look. Timeline: replace → ← text with Long-Arrow icons on
each letter entry and the distribution bar summary.

Refs: #179

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/routes/briefwechsel/ConversationTimeline.svelte

@@ -84,8 +84,24 @@ const newDocUrl = $derived(
 		aria-label="Briefverteilung in diesem Zeitraum: {outCount} von {senderName ?? ''}, {inCount} von {receiverName ?? ''}"
 	>
 		<div class="flex justify-between text-sm font-bold">
-			<span class="text-primary">{outCount} von {shortSenderName} →</span>
+			<span class="inline-flex items-center gap-1 text-primary"
-			<span class="text-accent">{inCount} von {shortReceiverName} ←</span>
+				>{outCount} von {shortSenderName}
+				<img
+					src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Right-MD.svg"
+					alt=""
+					aria-hidden="true"
+					class="inline h-3.5 w-3.5 opacity-60"
+				/></span
+			>
+			<span class="inline-flex items-center gap-1 text-accent"
+				>{inCount} von {shortReceiverName}
+				<img
+					src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Left-MD.svg"
+					alt=""
+					aria-hidden="true"
+					class="inline h-3.5 w-3.5 opacity-60"
+				/></span
+			>
 		</div>
 		<div class="flex h-[5px] overflow-hidden rounded-full bg-line">
 			<div class="h-full bg-primary transition-all" style="width: {outPct}%"></div>
@@ -115,14 +131,14 @@ const newDocUrl = $derived(
 			class:border-l-primary={isOut}
 			class:border-l-accent={!isOut}
 		>
-			<span
+			<img
-				class="w-[16px] shrink-0 text-sm font-black"
+				src={isOut
-				class:text-primary={isOut}
+					? '/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Right-MD.svg'
-				class:text-accent={!isOut}
+					: '/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Left-MD.svg'}
+				alt=""
 				aria-hidden="true"
-			>
+				class="h-4 w-4 shrink-0 opacity-60"
-				{isOut ? '→' : '←'}
+			/>
-			</span>
 
 			<div class="min-w-0 flex-1">
 				<div class="mb-[2px] truncate text-sm font-bold text-ink">

frontend/src/routes/briefwechsel/CorrespondenzPersonBar.svelte

@@ -91,22 +91,20 @@ function handleSuggestionSelect(id: string) {
 		class:pointer-events-none={!swapVisible}
 		tabindex={swapVisible ? 0 : -1}
 	>
-		<svg
+		<div class="-my-1 flex flex-col items-center">
-			xmlns="http://www.w3.org/2000/svg"
+			<img
-			width="14"
+				src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Right-MD.svg"
-			height="14"
+				alt=""
-			viewBox="0 0 24 24"
+				aria-hidden="true"
-			fill="none"
+				class="h-3.5 w-3.5 opacity-60"
-			stroke="currentColor"
+			/>
-			stroke-width="2"
+			<img
-			stroke-linecap="round"
+				src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Left-MD.svg"
-			stroke-linejoin="round"
+				alt=""
-			aria-hidden="true"
+				aria-hidden="true"
-			class="rotate-90"
+				class="h-3.5 w-3.5 opacity-60"
-		>
+			/>
-			<path d="M7 16V4m0 0L3 8m4-4l4 4" />
+		</div>
-			<path d="M17 8v12m0 0l4-4m-4 4l-4-4" />
-		</svg>
 	</button>
 
 	<!-- Korrespondent field -->