Locally stored thumbnails for video and YouTube uploads

- Server-side video thumbnails: ffmpeg-static grabs a frame at ~1s,
  scales it to 480px and stores it under /uploads/thumbs/ at upload
  time (direct files, remote URLs and comment attachments)
- YouTube thumbnails are downloaded once at upload time instead of
  being hotlinked from i.ytimg.com on every render; remote URL kept
  as fallback for legacy rows
- thumbUrl now covers video/audio/youtube/twitch in grid meta,
  profile uploads and notifications
- Generated thumbnail files are removed on single/bulk delete

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

server/api/uploads/[id]/comments.post.ts

@@ -3,7 +3,7 @@ import { extname, join } from 'node:path'
 import { eq, sql } from 'drizzle-orm'
 import { z } from 'zod'
 import { commentAttachments, comments, uploads } from '../../../db/schema'
-import { isAudioAttachment, MAX_COMMENT_ATTACHMENTS } from '~~/shared/utils/attachments'
+import { isAudioAttachment, isVideoAttachment, MAX_COMMENT_ATTACHMENTS } from '~~/shared/utils/attachments'
 
 const bodySchema = z.object({
   content: z.string().trim().min(1).max(2000),
@@ -82,6 +82,9 @@ export default defineEventHandler(async (event) => {
       const audioMeta = !file.voice && isAudioAttachment({ mimeType, name: filename })
         ? await extractAudioMeta(`att-${commentId}-${i}`, data, mimeType)
         : null
+      const videoThumb = !file.voice && isVideoAttachment({ mimeType, name: filename })
+        ? await extractVideoThumb(`att-${commentId}-${i}`, join(attachmentsDir(), storedName))
+        : null
       const meta = file.voice ? { voice: true } : (audioMeta?.meta ?? null)
       const [row] = await db.insert(commentAttachments).values({
         commentId,
@@ -89,7 +92,7 @@ export default defineEventHandler(async (event) => {
         originalName: filename.slice(0, 255),
         mimeType,
         size: data.length,
-        cover: audioMeta?.cover ?? null,
+        cover: videoThumb ?? audioMeta?.cover ?? null,
         meta,
       })
       attachments.push({
@@ -98,7 +101,7 @@ export default defineEventHandler(async (event) => {
         url: `/uploads/attachments/${storedName}`,
         mimeType,
         size: data.length,
-        cover: audioMeta?.cover ?? null,
+        cover: videoThumb ?? audioMeta?.cover ?? null,
         meta,
       })
     }