The main timeline is the only time control; the Weather panel shows its frame time

The Weather panel kept a second time transport of its own: a slider, step
buttons, Latest and Play, backed by a replay in the weather clock that
stepped the observed frames every two seconds and went round from the last
to the first. The weather clock also attached itself to the world clock as
a driver, so the timeline's Play became that replay whenever weather was on.

The panel now shows the frame time only: the newest frame and its age while
live, the timeline time alone at a past time. The weather clock no longer
has setTarget, step, latest, play, pause or togglePlay, its state no longer
has playing, and it no longer drives the world clock. It still follows the
world time, registers each product's frames as marks the timeline's arrow
keys step to, holds its products, and gates the world's continuous play at
each next frame until it loads. weatherClock.world names the world clock it
follows.

A weather row's play, latest and step params move the world clock as the
timeline does: play toggles continuous play (from the start of the covered
time when live), latest goes live, and step goes to the previous or next
mark. The rail timeline component, which only the panel used, is removed,
along with its unused messages in every locale.

docs/VUE-MIGRATION.md

@@ -153,9 +153,9 @@ a feature supplying only its accent.
    `t()`, which follows the locale as the view renders; the views carry no
    `data-i18n*` markers, which `npm run i18n` rejects in a template. Shared builders become components first and
    keep their imperative entry points until their owners are components:
-   the rail cards, card blocks and timeline (`src/ui/rail/`) render through
-   Vue's synchronous `render()` behind `createRailCards()`,
-   `createRailCardBlocks()` and `createRailTimeline()`. Order: Scenes (done: `SceneOptions` and
+   the rail cards and card blocks (`src/ui/rail/`) render through
+   Vue's synchronous `render()` behind `createRailCards()` and
+   `createRailCardBlocks()`. Order: Scenes (done: `SceneOptions` and
    `SceneShotList` over the `gev-scenes` store; the panel's buttons, status
    line, progress bar and the runtime chip render the panel SceneControls
    presents there, and the buttons and file chooser call its actions), Weather (done: the owner