feat(mentor-workspace): inline document preview matching applicant docs pattern

- Eye toggle expands the row below to embed FilePreview from
  @/components/shared/file-viewer (PDF iframe, image, video, Office docs)
- Download button uses explicit Content-Disposition: attachment via a
  new `disposition` input on workspaceGetFileDownloadUrl
- getPresignedUrl learns `inline: true` and optional `response-content-type`
  override so PDFs/images don't get force-downloaded by MinIO's default
- Eye button only renders for previewable mime types

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/server/routers/mentor.ts

@@ -2307,16 +2307,21 @@ export const mentorRouter = router({
    * Issue a short-lived presigned GET URL to download a workspace file.
    */
   workspaceGetFileDownloadUrl: protectedProcedure
-    .input(z.object({ mentorFileId: z.string() }))
+    .input(z.object({
+      mentorFileId: z.string(),
+      disposition: z.enum(['inline', 'attachment']).default('attachment'),
+    }))
     .mutation(async ({ ctx, input }) => {
       const file = await ctx.prisma.mentorFile.findUnique({
         where: { id: input.mentorFileId },
-        select: { bucket: true, objectKey: true, fileName: true, projectId: true },
+        select: { bucket: true, objectKey: true, fileName: true, mimeType: true, projectId: true },
       })
       if (!file) throw new TRPCError({ code: 'NOT_FOUND', message: 'File not found' })
       await assertProjectWorkspaceAccess(ctx.prisma, ctx.user.id, file.projectId)
       const url = await getPresignedUrl(file.bucket, file.objectKey, 'GET', 900,
-        { downloadFileName: file.fileName })
+        input.disposition === 'inline'
+          ? { inline: true, contentType: file.mimeType }
+          : { downloadFileName: file.fileName })
       return { url }
     }),