feat(desktop): let the status bar be hidden

[OutThisLife]

The status bar is always-on chrome today. This makes it something you can put
away, defaulting on and remembering the choice per window profile.

Three doors, matching the set VS Code offers: ⌘⇧S (rebindable in the keybinds
panel), the ⌘K palette, and a "Hide status bar" row at the bottom of the bar's
own right-click menu. The palette entry matters more than it looks — hiding the
bar removes the surface that would otherwise offer it back, so it's the
guaranteed way in. The context-menu row carries a live keybind hint for the same
reason, and that menu now renders even when no item opted into the existing
show/hide checkbox list.

On the keybinding: VS Code ships workbench.action.toggleStatusbarVisibility
with no default at all, because their ⌘K layout commands are two-stroke chords
and ⌘K ⌘S is already Keyboard Shortcuts. Hermes has no chord dispatcher, so
this takes the nearest free single combo instead. mod+shift+s is Cmd on macOS
and Ctrl elsewhere, and collides with nothing on either platform — worth noting
that canonicalizeCombo folds literal ctrl+* bindings into mod+* off macOS,
so a ctrl+shift+s elsewhere in the map would have collided on Windows/Linux
but not on a Mac. There isn't one. It sits with the other view.toggle* singles
(⌘B, ⌘J, ⌘G).

Hidden unmounts the bar rather than hiding it with CSS, so its 15s status poll
and the per-turn readouts stop along with it.

Pane tab strips

Second commit, same surface-level theme. The pane tab strips painted with
--theme-card-seed — the raw, unmixed seed rather than a surface token — so
they read as their own band beside the sidebar and titlebar, which share
--ui-bg-sidebar.

This is fixed at the default in PaneTab rather than per strip, because the
right-rail preview strip never set the vars at all: its container was already on
the sidebar surface while its inactive tabs fell through to the seed. Correcting
the fallback fixes that strip for free and keeps the next one from regressing.
With the default right, the two zone strips no longer need to redeclare the var
and paint the token directly.

Active tabs stay legible on the flattened strip — the horizontal ones keep the
2px --theme-primary underline and text-foreground, and the vertical rail's
active tab still sits on the editor surface.

Test plan

• npm run typecheck clean
• npx eslint clean on changed files
• npx vitest run src/app/shell/statusbar-visibility.test.tsx src/components/ui/pane-tab.test.tsx — 13/13
• hgui: ⌘⇧S hides the bar and the workspace grows into the row; ⌘K "status bar" brings it back; right-click row shows the live hint
• hgui: pane header, collapsed vertical rail, and right-rail preview strip all read as one surface with the sidebar and titlebar

[github-actions]

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ℹ️ Info

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