A pin on the title bar, and no more notch

Pointing at a tile's top edge already brings its bar back, which left the
notch doing half a job: it could still hide a bar, but hiding one tile at a
time stopped being the interesting question once the whole dashboard could
fold its bars at once. It is gone.

In its place, a pin beside each tile's label. Pinned, that tile keeps its
bar while auto-hide is on — for the one or two tiles whose controls are
wanted at a glance. It sits next to the label rather than out with the gear
and ✕ because it is about the bar, not about the tile's contents, and it
stays faint until the tile is pointed at or the pin is on, so a wall of
unpinned tiles is not a wall of pins.

Fullscreen keeps its own rule: every bar folds, pinned or not, because that
is a mode for watching. What it loses with the notch it gets back better —
the same hover at a tile's top edge peeks a bar there too, and now as an
overlay, so peeking no longer pushes the tile's content down and disturbs
the auto-fit. The peek timer the notch needed goes with it.

Per-tile `headHidden` gives way to `headPinned` in the layout, on disk and
on the server.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

server.js

@@ -1411,7 +1411,7 @@ function sanitizeLayout(raw) {
         // card, and a solo timer comes back with a full tile's settings.
         variant: String(t?.variant || ''),
         title: String(t?.title || ''),
-        headHidden: Boolean(t?.headHidden),
+        headPinned: Boolean(t?.headPinned),
       };
       if (Number(t?.minSize?.w) > 0 && Number(t?.minSize?.h) > 0) {
         tile.minSize = { w: Number(t.minSize.w), h: Number(t.minSize.h) };