[mfuntowicz]

The flyout could only be dismissed by clicking away (deactivation) —
there was no keyboard path at all. Copy the overlay window's in-repo
pattern: wrap the root Grid in a UserControl (KeyboardAccelerators live
on Control, not Window) with a window-level Escape accelerator that
hides the flyout, firing regardless of which element has focus.

Stack (merge in order, top first):

1. fix(ui): wire the download cancel button into the row action cell #18 — fix(ui): wire the download cancel button into the row action cell
2. fix(ui): surface model load failures instead of failing silently #19 — fix(ui): surface model load failures instead of failing silently
3. fix(ui): make the empty-state text honest in every server state #20 — fix(ui): make the empty-state text honest in every server state
4. fix(ui): dismiss the tray flyout with Esc #21 — fix(ui): dismiss the tray flyout with Esc
5. feat(ui): show bytes, speed and ETA while a model downloads #22 — feat(ui): show bytes, speed and ETA while a model downloads
6. feat(ui): preflight disk space and show sizes on Recommended rows #23 — feat(ui): preflight disk space and show sizes on Recommended rows
7. fix(ui): make Recommended rows keyboard- and screen-reader-reachable #24 — fix(ui): make Recommended rows keyboard- and screen-reader-reachable
8. fix(ui): surface LlamaManager.FailureMessage instead of dropping it #25 — fix(ui): surface LlamaManager.FailureMessage instead of dropping it
9. feat(ui): first-run guidance — install indication and hotkey discovery #26 — feat(ui): first-run guidance — install indication and hotkey discovery
10. fix(ui): smaller UX items — wording, glyphs, featured order, descriptions, logs #27 — fix(ui): smaller UX items — wording, glyphs, featured order, descriptions, logs