Vendor backend and frontend into the monorepo

The submodule collapse was only half applied: .gitmodules was deleted but
backend/ and frontend/ were still recorded as gitlinks, so none of their
files were tracked. Replace the gitlinks with the real trees.

Also untrack .env (it carried placeholder secrets) in favour of a tracked
.env.example, drop the committed __pycache__, and narrow the blanket *.png
ignore that would have swallowed design assets.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/components/ui/tooltip.tsx

@@ -0,0 +1,59 @@
+import * as React from "react"
+import * as TooltipPrimitive from "@radix-ui/react-tooltip"
+
+import { cn } from "@/lib/utils"
+
+function TooltipProvider({
+  delayDuration = 0,
+  ...props
+}: React.ComponentProps<typeof TooltipPrimitive.Provider>) {
+  return (
+    <TooltipPrimitive.Provider
+      data-slot="tooltip-provider"
+      delayDuration={delayDuration}
+      {...props}
+    />
+  )
+}
+
+function Tooltip({
+  ...props
+}: React.ComponentProps<typeof TooltipPrimitive.Root>) {
+  return (
+    <TooltipProvider>
+      <TooltipPrimitive.Root data-slot="tooltip" {...props} />
+    </TooltipProvider>
+  )
+}
+
+function TooltipTrigger({
+  ...props
+}: React.ComponentProps<typeof TooltipPrimitive.Trigger>) {
+  return <TooltipPrimitive.Trigger data-slot="tooltip-trigger" {...props} />
+}
+
+function TooltipContent({
+  className,
+  sideOffset = 0,
+  children,
+  ...props
+}: React.ComponentProps<typeof TooltipPrimitive.Content>) {
+  return (
+    <TooltipPrimitive.Portal>
+      <TooltipPrimitive.Content
+        data-slot="tooltip-content"
+        sideOffset={sideOffset}
+        className={cn(
+          "bg-foreground text-background animate-in fade-in-0 zoom-in-95 data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=closed]:zoom-out-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2 z-50 w-fit origin-(--radix-tooltip-content-transform-origin) rounded-md px-3 py-1.5 text-xs text-balance",
+          className
+        )}
+        {...props}
+      >
+        {children}
+        <TooltipPrimitive.Arrow className="bg-foreground fill-foreground z-50 size-2.5 translate-y-[calc(-50%_-_2px)] rotate-45 rounded-[2px]" />
+      </TooltipPrimitive.Content>
+    </TooltipPrimitive.Portal>
+  )
+}
+
+export { Tooltip, TooltipTrigger, TooltipContent, TooltipProvider }