feat(ui): restore sidebar chrome, delete the pane workspace strip, compact native narrow header (#103561)

* feat(ui): restore sidebar chrome and remove the pane workspace strip

Reverse course from #103426 on the app chrome: the left sidebar owns
brand, pinned navigation + More, New session, sessions, and the footer
(status dot, Settings, Docs, pairing, theme) again, and the desktop
topbar is gone. What stays from that PR: the dockable workspace rail
(right/bottom, drag or button), the in-flow split-pane headers, and
Cmd+B now hides the sidebar entirely (no 78px icon rail) with a
floating expand control.

The real target of the original request: the vertical icon strip at
each pane's right edge is deleted. A collapsed workspace rail renders
nothing; the toggle (with a changed-file badge) lives in the split-pane
header next to split/close, or floats at the top-right in single-pane
chat. Shift+Cmd+B still toggles.

Narrow native macOS windows (e.g. the in-app link browser splitting
the window) previously stacked 50px of injected titlebar padding on
top of the 58px drawer row; the web CSS now folds that into one
compact 58px row beside the traffic lights, with selectors that
outrank the rules shipped Mac apps inject.

* chore(ui): regenerate locale bundles and docs map for sidebar restore

* fix(ui): bind showPaneHeader explicitly on the classic single pane

* chore(ui): reconcile locale metadata after rebase onto lobster wild cards

docs/docs_map.md

@@ -9923,7 +9923,7 @@ Do not edit it by hand; run `pnpm docs:map:gen`.
   - H2: Gateway host status
   - H2: Language support
   - H2: Appearance themes
-  - H2: Navigation
+  - H2: Sidebar navigation
   - H2: What it can do (today)
   - H2: MCP page
   - H2: Activity tab