feat(frontend): add image preview and prev/next navigation

frontend/src/lib/components/FilePreview.svelte

@@ -2,16 +2,45 @@
     import type { FileRecord } from '$lib/types';
     import { fade } from 'svelte/transition';
     import VideoPreview from './VideoPreview.svelte';
+    import ImagePreview from './ImagePreview.svelte';
+
+    let {
+        file,
+        onclose,
+        onprev,
+        onnext,
+        hasPrev = false,
+        hasNext = false
+    }: {
+        file: FileRecord;
+        onclose: () => void;
+        onprev?: () => void;
+        onnext?: () => void;
+        hasPrev?: boolean;
+        hasNext?: boolean;
+    } = $props();
 
-    let { file, onclose }: { file: FileRecord; onclose: () => void } = $props();
     const isVideo = $derived(file.fileType.includes('video'));
-</script>
+    const isImage = $derived(file.fileType.includes('image'));
 
-<svelte:window
+    $effect(() => {
-    onkeydown={(e) => {
+        function onKeydown(e: KeyboardEvent) {
-        if (e.key === 'Escape') onclose();
+            if (e.key === 'Escape') {
-    }}
+                onclose();
-/>
+            } else if (e.key === 'ArrowLeft' && hasPrev) {
+                e.preventDefault();
+                e.stopPropagation();
+                onprev?.();
+            } else if (e.key === 'ArrowRight' && hasNext) {
+                e.preventDefault();
+                e.stopPropagation();
+                onnext?.();
+            }
+        }
+        window.addEventListener('keydown', onKeydown, { capture: true });
+        return () => window.removeEventListener('keydown', onKeydown, { capture: true });
+    });
+</script>
 
 <!-- svelte-ignore a11y_click_events_have_key_events -->
 <!-- svelte-ignore a11y_no_static_element_interactions -->
@@ -20,12 +49,73 @@
     onclick={onclose}
     transition:fade={{ duration: 150 }}
 >
+    {#if hasPrev}
+        <button
+            class="absolute top-1/2 left-4 z-10 -translate-y-1/2 cursor-pointer rounded-full bg-black/40 p-2 text-white/70 transition-colors hover:bg-black/60 hover:text-white"
+            onclick={(e) => {
+                e.stopPropagation();
+                onprev?.();
+            }}
+            aria-label="Previous"
+        >
+            <svg
+                xmlns="http://www.w3.org/2000/svg"
+                class="h-5 w-5"
+                viewBox="0 0 24 24"
+                fill="none"
+                stroke="currentColor"
+                stroke-width="2"
+                stroke-linecap="round"
+                stroke-linejoin="round"
+            >
+                <polyline points="15 18 9 12 15 6" />
+            </svg>
+        </button>
+    {/if}
+
+    {#if hasNext}
+        <button
+            class="absolute top-1/2 right-4 z-10 -translate-y-1/2 cursor-pointer rounded-full bg-black/40 p-2 text-white/70 transition-colors hover:bg-black/60 hover:text-white"
+            onclick={(e) => {
+                e.stopPropagation();
+                onnext?.();
+            }}
+            aria-label="Next"
+        >
+            <svg
+                xmlns="http://www.w3.org/2000/svg"
+                class="h-5 w-5"
+                viewBox="0 0 24 24"
+                fill="none"
+                stroke="currentColor"
+                stroke-width="2"
+                stroke-linecap="round"
+                stroke-linejoin="round"
+            >
+                <polyline points="9 18 15 12 9 6" />
+            </svg>
+        </button>
+    {/if}
+
     <div
-        class="relative aspect-video h-[85vh] max-w-[95vw] overflow-hidden rounded-xl border border-sky-200/20 bg-[#0f1117]"
+        class="relative overflow-hidden rounded-xl border border-sky-200/20 bg-[#0f1117] {isImage
+            ? 'max-h-[85vh] max-w-[95vw]'
+            : 'aspect-video h-[85vh] max-w-[95vw]'}"
         onclick={(e) => e.stopPropagation()}
     >
+        {#key file.id}
             {#if isVideo}
                 <VideoPreview src={`/api/files/${file.id}/stream_part`} />
+            {:else if isImage}
+                <ImagePreview src={`/api/files/${file.id}/download`} alt={file.name} />
+            {:else}
+                <div class="flex h-full w-full items-center justify-center text-sm text-white/40">
+                    No preview available
+                </div>
+            {/if}
+        {/key}
+
+        {#if isVideo || isImage}
             <div
                 class="pointer-events-none absolute inset-x-0 top-0 z-10 flex items-center justify-between bg-linear-to-b from-black/70 to-transparent px-4 py-3"
             >
@@ -52,10 +142,6 @@
                     </svg>
                 </button>
             </div>
-        {:else}
-            <div class="flex h-full w-full items-center justify-center text-sm text-white/40">
-                No preview available
-            </div>
         {/if}
     </div>
 </div>

frontend/src/lib/components/ImagePreview.svelte

@@ -0,0 +1,5 @@
+<script lang="ts">
+    let { src, alt }: { src: string; alt: string } = $props();
+</script>
+
+<img {src} {alt} class="block max-h-[85vh] max-w-[95vw] object-contain" />

frontend/src/routes/+page.svelte

@@ -29,6 +29,27 @@
         fileRecords.filter((f) => f.name.toLowerCase().includes(search.toLowerCase()))
     );
 
+    let previewIndex = $derived.by(() => {
+        if (!previewFile) {
+            return -1;
+        }
+        const id = previewFile.id;
+        return filteredFileRecords.findIndex((f) => f.id === id);
+    });
+    let hasPrev = $derived(previewIndex > 0);
+    let hasNext = $derived(previewIndex >= 0 && previewIndex < filteredFileRecords.length - 1);
+
+    function goPrev() {
+        if (hasPrev) {
+            previewFile = filteredFileRecords[previewIndex - 1];
+        }
+    }
+    function goNext() {
+        if (hasNext) {
+            previewFile = filteredFileRecords[previewIndex + 1];
+        }
+    }
+
     let fileInput: HTMLInputElement;
 
     async function handleUpload(event: Event) {
@@ -214,5 +235,12 @@
 </div>
 
 {#if previewFile}
-    <FilePreview file={previewFile} onclose={() => (previewFile = null)} />
+    <FilePreview
+        file={previewFile}
+        onclose={() => (previewFile = null)}
+        onprev={goPrev}
+        onnext={goNext}
+        {hasPrev}
+        {hasNext}
+    />
 {/if}