feat: replace header dropdowns with collapsible sidebar tree

- Add Sidebar.tsx: project/session tree with inline rename, collapse/resize
- App.tsx: load all sessions at startup, sync selectedProject on session click
- Header.tsx: strip project/session UI, keep only right-side controls
- globals.css: add .main-layout, sidebar, item, and activity-dot styles
- Chat pane: move toggle button to left, use triangle icons matching sidebar

1 files changed, 2 insertions, 2 deletions

diff --git a/renderer/src/components/ChatPane.tsx b/renderer/src/components/ChatPane.tsx
index c2cdfbb..4136d16 100644
--- a/renderer/src/components/ChatPane.tsx
+++ b/renderer/src/components/ChatPane.tsx
@@ -45,10 +45,10 @@ export function ChatPane({
       style={{ width: collapsed ? 28 : chatWidth }}
     >
       <div className="chat-header">
-        {!collapsed && <span>Chat</span>}
         <button className="chat-collapse-btn" onClick={onToggleCollapse}>
-          {collapsed ? "⟨" : "⟩"}
+          {collapsed ? "â—€" : "â–·"}
         </button>
+        {!collapsed && <span>Chat</span>}
       </div>
 
       {!collapsed && (