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/files.rs

@@ -9,7 +9,7 @@ use super::{Tree, TreeNode};
 use crate::{
     data_display::Tone,
     forms::{SearchInput, TextInput},
-    primitives::IconName,
+    primitives::{IconName, file_icon},
     theme::ControlSize,
 };
 
@@ -57,19 +57,6 @@ impl GitStatus {
     }
 }
 
-/// The icon a file's name suggests.
-fn icon_for(name: &str) -> IconName {
-    let kind = name.rsplit_once('.').map(|(_, kind)| kind.to_lowercase());
-    match kind.as_deref() {
-        Some("rs" | "ts" | "tsx" | "js" | "py" | "go" | "swift" | "c" | "h" | "sh") => {
-            IconName::Code
-        }
-        Some("png" | "jpg" | "jpeg" | "gif" | "svg" | "webp") => IconName::Image,
-        Some("toml" | "json" | "yaml" | "yml" | "lock") => IconName::SlidersHorizontal,
-        _ => IconName::FileText,
-    }
-}
-
 /// A folder of the tree being built: its folders and its files, each by name.
 #[derive(Default)]
 struct Folder {
@@ -141,7 +128,7 @@ fn nodes(
         files.sort_by_key(|name| name.to_lowercase());
         for name in files {
             let path = format!("{prefix}{name}");
-            let node = TreeNode::new(path.clone(), name.clone()).icon(icon_for(name));
+            let node = TreeNode::new(path.clone(), name.clone()).icon(file_icon(name));
             out.push(match state(&path) {
                 Some(state) => {
                     changed = true;