feat: move projects to sidebar rail and speed up session switching (#506)

* feat: move projects from header tabs to left sidebar rail

* refactor: remove variant from git generation session context

* feat: implemented drandrop action for navrails

* refactor: improve sidebar drag-and-drop smoothness and remove floating overlay

* fix: prevent mobile nav rail touch from closing drawer and opening menu

* fix: hide header tabs on desktop

* fix: prevent session flicker when switching projects

* style: soften chat panel divider borders

* style: improve icon contrast across core navigation

* fix: stabilize session selection during project switching

* style: unify sidebar surfaces and transparent section layers

* style: remove UI shadows and keep only scroll shadow

* perf: speed up project switching with cached session loading

* perf: speed up Git changes view and background refresh

* perf: make session switching lighter and less aggressive

* perf: optimized sessions list loading while project switching

* perf: smooth chat rendering and reduce interaction spikes

* fix: restore reliable load older messages visibility

packages/ui/src/components/chat/message/TextSelectionMenu.tsx

@@ -321,7 +321,7 @@ export const TextSelectionMenu: React.FC<TextSelectionMenuProps> = ({ containerR
         className={cn(
           'flex items-center gap-1',
           'rounded-lg border border-[var(--interactive-border)]',
-          'bg-[var(--surface-elevated)] shadow-lg',
+          'bg-[var(--surface-elevated)] shadow-none',
           'px-1.5 py-1',
           'transition-[opacity,transform] duration-200 ease-out will-change-[opacity,transform]',
           isClosing