Merge christianhaberl's session-sidebar branch, ported to current master

Brings in https://github.com/christianhaberl/Codeman/pull/4 (three commits,
authorship preserved) and adapts it across the 211 commits master gained
since the branch was cut:

- App Settings control re-authored for the set-* surface (PR #278): a
  set-row in Layout -> Tabs, replacing the old settings-item markup the
  branch targeted. i18n description synced.
- Lineage arcs (PR #291, post-branch) are SKIPPED in sidebar layout:
  computeLineagePath()'s U-bridge geometry hangs from the horizontal
  strip's bottom edge and has no meaning against a vertical list. The
  lineage strip-scroll listener now also redraws subagent/ultracode
  connectors while the sidebar scrolls vertically.
- The desktop home tab rail (post-branch) defers to the sidebar: both dock
  the session list flush left, and the rail would render z-ordered under it.
- Active-row reveal unified into _scrollActiveTabIntoView() (#257 landed on
  master after the branch): sidebar mode branches to scrollIntoView
  block:'nearest', and _fullRenderSessionTabs() restores scrollTop alongside
  the #257 scrollLeft restore so ambient rebuilds cannot yank a mid-scroll
  sidebar back to the top.
- Mobile active-tab hoisting the branch guarded against no longer exists on
  master (removed by #257); kept master's order-stable render.

Verified: typecheck, lint, format:check, check:frontend-syntax,
check:public-assets, PostCSS parse of both merged stylesheets, the 26 new
jsdom tests, the structural guard suites, and the headless-Chromium harness
(scripts/verify-session-sidebar.mts) green across all seven layout states
at 1600/1000/393px against current master.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/settings-ui.js

@@ -387,6 +387,8 @@ Object.assign(CodemanApp.prototype, {
     document.getElementById('appSettingsExtendedKeyboardBar').checked = settings.extendedKeyboardBar ?? false;
     document.getElementById('appSettingsTabTwoRows').checked = settings.tabTwoRows ?? defaults.tabTwoRows ?? false;
     document.getElementById('appSettingsShowTabDetachButton').checked = settings.showTabDetachButton ?? defaults.showTabDetachButton ?? false;
+    document.getElementById('appSettingsSessionListLayout').value =
+      settings.sessionListLayout ?? defaults.sessionListLayout ?? 'header';
     // Claude CLI settings
     const claudeModeSelect = document.getElementById('appSettingsClaudeMode');
     const allowedToolsRow = document.getElementById('allowedToolsRow');
@@ -2007,6 +2009,7 @@ Object.assign(CodemanApp.prototype, {
       extendedKeyboardBar: document.getElementById('appSettingsExtendedKeyboardBar').checked,
       tabTwoRows: document.getElementById('appSettingsTabTwoRows').checked,
       showTabDetachButton: document.getElementById('appSettingsShowTabDetachButton').checked,
+      sessionListLayout: document.getElementById('appSettingsSessionListLayout').value,
       skin: document.getElementById('appSettingsSkin').value,
       // Claude CLI settings
       claudeMode: document.getElementById('appSettingsClaudeMode').value,
@@ -2151,7 +2154,9 @@ Object.assign(CodemanApp.prototype, {
     this.applyHeaderVisibilitySettings();
     this.applySkin();
     this.applyLocalization();
-    this.applyTabWrapSettings();
+    // Re-parents #sessionTabs between header host and sidebar if the layout
+    // changed, then calls applyTabWrapSettings() itself — do not call both.
+    this.applySessionListLayout();
     this.applyLineageLineSettings?.();
     this._updateTokensImmediate();  // Re-render token display (picks up showCost change)
     this.applyMonitorVisibility();
@@ -2389,6 +2394,7 @@ Object.assign(CodemanApp.prototype, {
         imageWatcherEnabled: false,
         ralphTrackerEnabled: false,
         tabTwoRows: false,
+        sessionListLayout: 'header',
         cjkInputEnabled: false,
         terminalWheelLocalScrollback: false, // mobile scrolls via touch, not wheel
         webglRendererEnabled: false, // mobile always uses the DOM renderer
@@ -2633,19 +2639,27 @@ Object.assign(CodemanApp.prototype, {
     const settings = this.loadAppSettingsFromStorage();
     const defaults = this.getDefaultSettings();
     const deviceType = MobileDetection.getDeviceType();
+    // The left sidebar is one vertical column with its own scroller: there is no
+    // row to wrap into, and its rows are always tall (name + folder) because that
+    // is the cheapest way to tell 25 sessions apart. Header strip keeps the old
+    // rules unchanged. Kept here rather than only in applySessionListLayout() so
+    // that a stray applyTabWrapSettings() call (this one is invoked from
+    // saveAppSettings and from the resize path) cannot leave the sidebar wrapped.
+    const sidebar = this.isSessionSidebarActive?.() === true;
     // Two-row tabs disabled on mobile/tablet — not enough screen space
-    const twoRows = deviceType === 'desktop'
+    const twoRows = !sidebar && deviceType === 'desktop'
       ? (settings.tabTwoRows ?? defaults.tabTwoRows ?? false)
       : false;
+    const showFolder = sidebar || twoRows;
     const prevTallTabs = this._tallTabsEnabled;
-    this._tallTabsEnabled = twoRows;
+    this._tallTabsEnabled = showFolder;
     const tabsEl = document.getElementById('sessionTabs');
     if (tabsEl) {
       tabsEl.classList.toggle('tabs-two-rows', twoRows);
-      tabsEl.classList.toggle('tabs-show-folder', twoRows);
+      tabsEl.classList.toggle('tabs-show-folder', showFolder);
     }
     // Re-render tabs if folder visibility changed (folder spans are generated in JS)
-    if (prevTallTabs !== undefined && prevTallTabs !== twoRows) {
+    if (prevTallTabs !== undefined && prevTallTabs !== showFolder) {
       this._fullRenderSessionTabs();
     }
   },
@@ -2850,7 +2864,7 @@ Object.assign(CodemanApp.prototype, {
           'showFontControls', 'showSystemStats', 'showTokenCount', 'showCost',
           'showLifecycleLog', 'showResponseViewer', 'showRedrawButton',
           'showMonitor', 'showProjectInsights', 'showFileBrowser', 'showSubagents',
-          'subagentActiveTabOnly', 'tabTwoRows', 'localEchoEnabled', 'cjkInputEnabled', 'extendedKeyboardBar',
+          'subagentActiveTabOnly', 'tabTwoRows', 'sessionListLayout', 'localEchoEnabled', 'cjkInputEnabled', 'extendedKeyboardBar',
           'skin', 'showPlanUsageLimits', 'showAttachmentsButton', 'showFileViewerButton', 'webglRendererEnabled',
           'language',
           'terminalWheelLocalScrollback',