feat: narrow-window behavior — sidebar auto-close, chrome wrap, 640px floor

The sidebar no longer squeezes the page when the window narrows; the
page itself never goes below a comfortable floor (owner decisions,
2026-09-17: 640px min, widen-window on toggle, auto-restore):

- minWidth 640 / minHeight 600 on the BrowserWindow (macOS enforces)
- Below SIDEBAR_AUTOCLOSE (928 = 640 + 288 sidebar) the sidebar
  auto-closes, and auto-RESTORES when the window widens past it again —
  both fall out of one expression: rendered = pref && !narrow, where
  pref is the persisted user choice. Manual closes persist and stay
  closed; auto-close never touches the preference.
- Opening the sidebar while narrow asks the shell to widen the window
  to 928 first (new lh:expand-window IPC, preload.cjs contextBridge —
  the renderer's first and only Electron bridge): the toggle is never a
  dead button, and the layout never has to survive narrow + sidebar.
  In the plain browser there is no suppression and no widening — a
  narrow tab opens the sidebar if the user says so.
- Graph chrome row wraps: max-w-[calc(100%-9rem)] + flex-wrap keeps the
  row clear of the header toggle cluster and stacks it onto extra lines
  below ~640px instead of overflowing left.

State machine verified in the Electron dev shell across all six
transitions (auto-close, auto-restore, manual-close-persists,
reopen-widens, browser fallback, wrap at 640/500/360).

components/graph-view.tsx

@@ -973,8 +973,12 @@ export function GraphView() {
 			    lh-no-drag (2026-09-17): home.tsx's floating drag strip
 			    underlays this row — Electron's drag mask ignores z-index,
 			    so without an explicit carve-out the controls were
-			    unclickable in the desktop app (owner report). */}
-			<div className="lh-no-drag absolute right-3 top-3 z-10 flex items-start gap-2">
+			    unclickable in the desktop app (owner report). max-w + flex-wrap
+			    (narrow-window wave, 2026-09-17): below the sidebar auto-close
+			    threshold the row wraps to a second line instead of overflowing
+			    left over the header toggle cluster (92px gutter + 36px button);
+			    9rem keeps one clear column of air alongside it. */}
+			<div className="lh-no-drag absolute right-3 top-3 z-10 flex max-w-[calc(100%-9rem)] flex-wrap items-start gap-2">
 				{!isEmpty && (
 					<>
 					{/* Search — its own container (icon + input + no-match note). */}