Files · Transfers: file operations, a transfer queue, downloads and storage

A file on its way is a Transfer with a state: waiting, moving at a rate,
paused, done or failed with a reason. One row draws it for the queue and
the downloads: its icon, its way, a bar while it moves or waits paused, a
status with the time left, and only the actions its state allows.
TransferQueue counts what moves and waits. DownloadManager keeps the
finished below under Clear, opening on a press and showing their folder.
FileOperationProgress tells a copy or move with its bar, time left and
current file, its header wrapping by the header rule; a failure speaks in
the danger tone. StorageUsage points to data_display's UsageBar.

TASKS.md

@@ -96,7 +96,7 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T26e Media · Capture and devices
 - [x] T27a Files · Items
 - [x] T27b Files · Explorer
-- [ ] T27c Files · Find and look
+- [x] T27c Files · Find and look
 - [ ] T27d Files · Transfers
 - [ ] T28 Messaging
 - [ ] T29 Mail
@@ -326,3 +326,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T27b | 1 | FAIL | the listing's fixed columns left no room for names at 280px; a column keyed by its depth handed its cursor to the next folder there |
 | T27b | 2 | PASS | |
 | T27c | 1 | FAIL | recent and found files were keyed by their place, so the cursor left a file an open moved |
+| T27c | 2 | PASS | |