feat: pinned rail component + cross-session focus

M4 of pinned terminals (v0.17.0):
- New PinnedRail component: compact strip above the tab bar, renders
  pinned terminals from other sessions (pin icon + terminal icon + title
  + tooltip with kind/scope/cwd)
- Click navigates to the home session (ctx.sessions.open) and activates
  the tab (or raises its float) via the pinnedJumpRef effect
- Right-click menu: Unpin / Close Terminal; middle-click close
- IconPinOutline16 added to icons.tsx
- Rail styles in sidebar.module.css (token-driven, no-drag opt-out)
- Sidebar: collectPinnedTabs on store snapshot + session list, railRevision
  state forces re-render after reduceFor (which doesn't notify)
- Cross-session close: reduceFor(closeTab/closeFloatByTab) + ptyClose/
  agentPtyClose; cross-session unpin: reduceFor(setTabPin null)

src/client/sidebar.module.css

@@ -458,6 +458,7 @@ body[data-dsh-sidebar-dragging] .bottomPanel {
 .toggleCluster,
 .toggleButton,
 .tabBar,
+.pinnedRail,
 .floatHeader {
   -webkit-app-region: no-drag;
 }
@@ -865,6 +866,87 @@ body[data-dsh-sidebar-dragging] .bottomPanel {
   color: var(--dsw-alias-label-primary);
 }
 
+/* ── Pinned-terminal rail (v0.17.0+) ──────────────────────────────────── */
+
+/* A compact strip above the tab bar showing pinned terminals from OTHER
+   sessions. Only renders when there is at least one visible pinned tab.
+   Hairline-separated from the tab bar below; token-driven so skins follow. */
+.pinnedRail {
+  flex: none;
+  display: flex;
+  align-items: stretch;
+  gap: 0;
+  padding: 0 4px;
+  border-bottom: 1px solid var(--dsw-alias-border-l1);
+  background: var(--dsw-alias-bg-layer-1);
+  overflow-x: auto;
+  scrollbar-width: none;
+}
+
+.pinnedRail::-webkit-scrollbar {
+  display: none;
+}
+
+.pinnedRailLabel {
+  flex: none;
+  display: inline-flex;
+  align-items: center;
+  padding: 0 6px 0 4px;
+  font: var(--dsw-font-xxxs-strong-11);
+  color: var(--dsw-alias-label-tertiary);
+  white-space: nowrap;
+}
+
+.pinnedTab {
+  flex: none;
+  display: inline-flex;
+  align-items: center;
+  gap: 4px;
+  max-width: 180px;
+  padding: 0 6px;
+  height: 28px;
+  font: var(--dsw-font-xxs-12);
+  color: var(--dsw-alias-label-secondary);
+  border-right: 1px solid var(--dsw-alias-border-l1);
+  background: transparent;
+  cursor: pointer;
+  user-select: none;
+  border-radius: 0;
+}
+
+.pinnedTab:hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+  color: var(--dsw-alias-label-primary);
+}
+
+.pinnedTabTitle {
+  flex: 1;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.pinnedTabClose {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  width: 16px;
+  height: 16px;
+  padding: 0;
+  border: none;
+  border-radius: 3px;
+  background: transparent;
+  color: var(--dsw-alias-label-tertiary);
+  cursor: pointer;
+  flex: none;
+}
+
+.pinnedTabClose:hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+  color: var(--dsw-alias-label-primary);
+}
+
 /* ── Explorer ──────────────────────────────────────────────────────────── */
 
 .explorer {