Capture · Roots: roots drop w_full; hosts give the width

145 component roots drop w_full, the early returns included. Three
field rows keep it, Input, InputGroup and TagInput: stretched without
a width, taffy 0.9 laid the field's flex_1 share at no width in the
template picker at 280px, and the placeholder drew nothing. Container
keeps it, since mx_auto needs a width to fill.

Hosts that relied on a root's width now give it: MessageList boxes
each row at the list's width, the splash gives its bar the column's,
and test stages that mount a component as the window's root sit in a
size_full box. Tests hold a narrow row across the list and the splash
bar across its column; each goes red without its fix.

The gallery gains --narrow <px>, which lays each page in a padded
card at that width and shoots it without its script. The page
header wraps: the title takes the room and the theme switcher drops
below, where a long summary used to push it past the edge. A file
panel step waits for the panel to become key instead of a fixed
pause, which lost a race in a capture.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TASKS.md

@@ -150,7 +150,7 @@ Per-component lines live in `tasks/`. Tags there:
 - [x] T43a Tooling · Workbench — `tasks/ch31-43.md`
 - [x] T43b Tooling · Inspection — `tasks/ch31-43.md`
 - [x] T43c Tooling · Catalogs — `tasks/ch31-43.md`
-- [ ] T44a Capture · Roots: roots still on `w_full` drop it; every section checked at 280px and in a padded card
+- [ ] T44a Capture · Roots: roots still on `w_full` drop it, checked at 280px and in padded cards
 - [ ] T44b Capture · Sections: every component's section shot on its own, light and dark, with a manifest the site reads
 - [ ] T44c Capture · Motion: clips of each page's scripted states in motion, for the site
 - [ ] T45 Website: `frontend/`, Vite 8, pnpm, light and dark: a home page in motion (three.js, smooth scroll), and a components page with every component, categories on the left and the chosen one's detail on the right, after astryx.atmeta.com