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/FileMentionAutocomplete.tsx

@@ -368,7 +368,7 @@ export const FileMentionAutocomplete = React.forwardRef<FileMentionHandle, FileM
   return (
       <div
         ref={containerRef}
-        className="absolute z-[100] min-w-0 w-full max-w-[520px] max-h-64 bg-background border-2 border-border/60 rounded-xl shadow-md bottom-full mb-2 left-0 flex flex-col"
+        className="absolute z-[100] min-w-0 w-full max-w-[520px] max-h-64 bg-background border-2 border-border/60 rounded-xl shadow-none bottom-full mb-2 left-0 flex flex-col"
         style={style}
       >
         {showTabs ? (
@@ -385,7 +385,7 @@ export const FileMentionAutocomplete = React.forwardRef<FileMentionHandle, FileM
                   className={cn(
                     'flex-1 px-2.5 py-1 rounded-md typography-meta font-semibold transition-none',
                     activeTab === tab.id
-                      ? 'bg-interactive-selection text-interactive-selection-foreground shadow-sm'
+                      ? 'bg-interactive-selection text-interactive-selection-foreground shadow-none'
                       : 'text-muted-foreground hover:bg-interactive-hover/50'
                   )}
                   onPointerDown={(event) => {