Let the library rail go down to 160px

[vmillet-dev]

The rail opened at 288px and would not be dragged under 220, which on a small window is a
third of it spent on a handful of short names.

That floor was never the tree's. space-editor and folder-editor both carry
min-width: 240px — what gives a dropdown a width at all — and the rail projects them
inline between its rows, so a narrower rail scrolled sideways and put the delete button
out of reach. The minimum is handed down as --editor-min-width instead, and the rail sets
it to 0: a custom property, because a rule spelled in the rail's own stylesheet is
rewritten with the rail's _ngcontent and can never reach into a component's (#207).

Fluid means the rows inside wrap rather than squeeze — .editor-form, .editor-delete-row,
.editor-colours and the rail's creation form take flex-wrap: wrap and a basis on the
field, so the button drops under it below about 230px and stays beside it above. Nothing
moves at the switchers' 240px. The floor is then 160, and so is the default: the width is
remembered like the window's own geometry, so the default is a first launch and nothing else,
and a profile that already holds 288 keeps it — asPixels clamps into the range, it does not
reset.

The ellipsis that was never there

Looking at the result rather than at the suite: a name too long came out cut mid-letter, no
ellipsis. text-overflow is a property of a block container and .node-name is a flex
one, which ignores it outright — the rule had been dead since the rail was written. It went
unseen because 288px never cut a name. The name lives in a .node-label of its own now.

Also pulled the folder panel back out of the 16px folder indent: at the floor those pixels
are the five colour swatches on one line rather than four and one.

Checks

npm run lint, npm test (1355), npm run build, npm run test:scripts, and the full e2e
suite — 22 spec files, including a new scenario in 05-spaces that narrows to the floor and
measures that the panel's controls are still inside the rail, which only a laid-out window
can say. Read the assembled application at 160px as well, panels open.

Closes #212

🤖 Generated with Claude Code

The rows line up, and the twisty is visible (second commit)

Two things the narrow rail made obvious. The ✦ sat inside the name of "all spaces",
so that one label started its own width plus a gap further right than every space under it;
it moves into the column the twisty already owns, and the two share a width, which is what
puts every name on one edge.

And ▾ is a small triangle by design — at the 12px the row's other marks use it drew a
speck nobody could identify. The size was read off the rendered pixels at 12 / 14 / 16 / 18 /
20px rather than guessed: 12 → 14 moved 72 pixels of the whole rail and changed nothing a
reader could see. It is 16px, where it reads as a triangle and still draws less ink than the
12.5px label beside it.

⚠️ Left alone deliberately: neither .node-twisty nor .node-menu takes hit-target, so
both sit under the 24×24 that WCAG 2.5.8 asks. Real, but pre-existing, and widening the first
column is the opposite of what this PR is for — worth its own ticket.