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.

tasks/ch21-30.md

@@ -287,23 +287,25 @@
 - [x] DeviceSelector
 - [x] 3DModelViewer — host frames, orbit input
 
-## T27 Files — `src/files`
+## T27a Files · Items — `src/files`
+
+- [x] FileIcon — one map from name to icon, in `primitives`
+- [x] FileItem
+- [x] FileList → `lists::DirectoryListing`
+- [x] FileGrid
+
+## T27b Files · Explorer
 
 - [ ] FileExplorer — list, icons, columns
-- [ ] FileGrid
-- [ ] FileList
-- [ ] FileItem
-- [ ] FileIcon
-- [ ] FilePreview / QuickLook
 - [ ] FileBreadcrumb / PathBar → `navigation::Breadcrumb`
 - [ ] FolderTree → `lists::FileTree`
 - [ ] FileContextMenu → `menus::ContextMenu`
 - [ ] RenameInline → `forms::InlineEdit`
 - [ ] DragDropFiles → `forms::DropZone`
-- [ ] FileOperationProgress
-- [ ] TransferQueue
-- [ ] DownloadManager
-- [ ] StorageUsage → `data_display::UsageBar`
+
+## T27c Files · Find and look
+
+- [ ] FilePreview / QuickLook
 - [ ] RecentFiles
 - [ ] Favorites / Bookmarks → `documents::Favorites`
 - [ ] FileSearch
@@ -311,6 +313,13 @@
 - [ ] ArchiveViewer — host entries
 - [ ] HexViewer → `debug::HexViewer`
 
+## T27d Files · Transfers
+
+- [ ] FileOperationProgress
+- [ ] TransferQueue
+- [ ] DownloadManager
+- [ ] StorageUsage → `data_display::UsageBar`
+
 ## T28 Messaging — `src/messaging`
 
 - [ ] ChannelList / ChatList