fix(ui): a caption never opens under a finger

On an iPad a tap's synthetic mouseenter opened the Tooltip; WebKit then took the
tap as a hover and swallowed its click, so every rail button needed two taps,
and with no mouseleave from a finger the caption stayed up. Tooltip now opens
for a mouse and a key's focus only (owner: no captions on touch).

docs/DESIGN.md

@@ -711,3 +711,4 @@ of a full-width panel and nothing on the right.
 | 2026-10-04 | E32 `field` focus skips a mode switch | A form opens on its first field; a control above it that is not a field (the composer's Edit / Preview) is passed over by marking the field `data-initial-focus` | The first text field everywhere | That moved the focus in the download dialog off its profile choice and in the upload dialog off its drop zone; the mark changes only the form that needs it |
 | 2026-10-04 | E35 Lint for z-levels and edged labels | Both rules stay; the two eslint selectors (`Z_RAW`, `EDGED_LABEL`) that refused them go | Keep the selectors | 0 hits since the E28 sweep that fixed the sites: a check that never fires costs a probe test and a snapshot each, and the UI review holds both rules |
 | 2026-10-06 | `player` focus | A dialog that is a player opens focused on its panel (the YouTube player's rule, now `Modal`'s too); on the media element itself, Space and the arrows stay the element's own | `close`, or the media element | On the ✕ Space closed the player; on the element the browser's own controls acted on the same key as the player's (one Space played and paused, measured in Chrome) |
+| 2026-10-08 | Captions on touch | A `Tooltip` opens for a mouse and a key's focus only, never for a finger | A caption on tap; a long-press caption | On an iPad the tap that showed the caption was taken as a hover and lost its click (every rail button took two taps), and no finger sends the mouseleave that hides it; the rail's labels setting names the buttons on touch |