feat: inline pinned tabs in TabBar (replaces PinnedRail)

M4 rewrite per user feedback: pinned terminals should display in the
Tabs bar itself, not a separate rail. Clicking activates in-place
(cross-session terminal rendering), no session jump.

Changes:
- Delete PinnedRail.tsx + tests/pinned-rail.spec.tsx
- pinned.ts: add createPinnedVirtualTab (virtual id = pinned:<sess>:<id>,
  meta.__pinnedHome = { sessionId, cwd, tabId }), injectPinnedIntoTree
  (appends virtual tabs to first leaf, overrides active), isPinnedVirtualId,
  parsePinnedVirtualId, isPinnedVirtualTab, getPinnedHomeScope
- tab-content-memo.ts: add effectiveTabId to memo key — TabContent passes
  the original tab id (not the virtual id) to the descriptor component so
  TerminalView's WS URL resolves to the home PTY
- Sidebar.tsx: augmented tree (injectPinnedIntoTree), activePinnedTabId
  state, wrappedActions (intercept virtual ids for activate/close/unpin/
  drag/float), renderTab passes home scope + effectiveTabId for pinned tabs,
  pinnedRevision replaces railRevision
- TabBar.tsx: pinned virtual tabs non-draggable, pin icon prefix, stripped
  context menu (Unpin/Close only, no float/close-others/left/right)
- sidebar.module.css: remove rail styles, add .pinnedTab (italic + tertiary)
- Docs: README/README_EN/AGENTS.md/design doc updated for inline approach

157/157 client-side tests pass; typecheck + build clean

src/client/sidebar.module.css

@@ -458,7 +458,6 @@ body[data-dsh-sidebar-dragging] .bottomPanel {
 .toggleCluster,
 .toggleButton,
 .tabBar,
-.pinnedRail,
 .floatHeader {
   -webkit-app-region: no-drag;
 }
@@ -866,85 +865,18 @@ 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;
-}
+/* ── Pinned-terminal tab (v0.17.0+) ───────────────────────────────────── */
 
+/* Pinned virtual tabs (injected from other sessions) render inline in the
+   tab bar with a pin icon and a subtle tint to distinguish them from the
+   session's own tabs. Token-driven so skins follow. */
 .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;
+  color: var(--dsw-alias-label-tertiary);
+  font-style: italic;
 }
 
 .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);
+  color: var(--dsw-alias-label-secondary);
 }
 
 /* ── Explorer ──────────────────────────────────────────────────────────── */