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/session-lineage.js

@@ -130,6 +130,14 @@ Object.assign(CodemanApp.prototype, {
   _appendLineageConnectionLines(svg, rects) {
     this._lineageEdgeCount = 0;
     if (!svg || !this._lineageLinesEnabled()) return;
+    // Sidebar layout: computeLineagePath()'s whole geometry — the U-bridge hung
+    // from the STRIP's bottom edge, the 64px dip corridor — assumes a horizontal
+    // tab row. Against a vertical list the "strip bottom" is the bottom of the
+    // sidebar, so every arc would draw a giant loop to the foot of the list.
+    // Parent/child adjacency reads fine in a vertical list without arcs; a
+    // sideways lineage shape is a follow-up with its own visual tuning, not a
+    // by-product of a layout port.
+    if (this.isSessionSidebarActive?.()) return;
     const compute = window.CodemanLineage && window.CodemanLineage.computePath;
     if (!compute) return;
 
@@ -203,7 +211,10 @@ Object.assign(CodemanApp.prototype, {
     const strip = document.getElementById('sessionTabs');
     if (!strip) return;
     this._lineageScrollHandler = () => {
-      if (this._lineageEdgeCount > 0) this.updateConnectionLines();
+      // Sidebar layout scrolls the SAME element vertically, and there the
+      // subagent/ultracode connectors anchor to tab rects too (lineage arcs are
+      // skipped, so _lineageEdgeCount alone would never redraw them).
+      if (this._lineageEdgeCount > 0 || this.isSessionSidebarActive?.()) this.updateConnectionLines();
     };
     strip.addEventListener('scroll', this._lineageScrollHandler, { passive: true });
   },