Files · Items: one icon map, file icon, file row and file grid

The crate had two maps from a file's name to its icon, in chat and in the
file tree, and they disagreed. One map now lives in primitives, over the
Lucide file-* icons, and chat, agent, the file tree and the directory
listing use it. FileIcon draws it for a file or a folder. FileItem is a
file's row, a ListItem with its size and when it changed. FileList is the
directory listing. FileGrid lays tiles in the order given, with a cursor
seeded from the owner's pick: arrows by tile and by row, Home, End, Enter
and a double press to open. The count of what fits a width has one home,
layout's columns_for, and fit builds on it.

src/lists/directory.rs

@@ -9,7 +9,7 @@ use jiff::Timestamp;
 use super::{ListItem, SelectableList};
 use crate::{
     navigation::{Breadcrumb, Crumb},
-    primitives::{Icon, IconName},
+    primitives::{Icon, IconName, file_icon},
     theme::{ActiveTheme, IconSize, TextSize},
     typography::{format, tabular},
 };
@@ -46,6 +46,15 @@ impl DirEntry {
     pub fn is_folder(&self) -> bool {
         self.size.is_none()
     }
+
+    /// A file's size in bytes; none for a folder.
+    pub fn size(&self) -> Option<u64> {
+        self.size
+    }
+
+    pub fn modified(&self) -> Timestamp {
+        self.modified
+    }
 }
 
 /// A column a listing sorts by.
@@ -223,7 +232,7 @@ impl RenderOnce for DirectoryListing {
                             Icon::new(if entry.is_folder() {
                                 IconName::Folder
                             } else {
-                                IconName::File
+                                file_icon(&entry.name)
                             })
                             .size(IconSize::Md)
                             .color(colors.fg_muted),