fix(panel): task-detail tab state in URL, nav placement, kanban overflow, sidebar divider, tooltip sweep

- Task detail: active tab lives in ?tab= (survives reload, back/forward, and
  prev/next task jumps); prev/next arrows move into the header row next to
  Actions instead of their own row above the title
- Constraints section always starts collapsed (project boilerplate)
- Kanban: native overflow scroll replaces Radix ScrollArea (display:table
  viewport let cards grow past the column and clip); columns share width
  (flex-1, 18rem floor, 24rem cap); dark column colors normalized to /40 tints
- Sidebar footer: drop the Separator doubled with the wrapper's border-t
- Tooltips: self-providing Tooltip root (300ms) + hover hints across sidebar,
  header, task detail, kanban, and every icon-only button that had none

panel/src/components/tasks/acceptance-criteria-editor.tsx

@@ -2,6 +2,11 @@
 
 import { useState } from "react";
 import { Button } from "@/components/ui/button";
+import {
+  Tooltip,
+  TooltipContent,
+  TooltipTrigger,
+} from "@/components/ui/tooltip";
 import { Input } from "@/components/ui/input";
 import { Label } from "@/components/ui/label";
 import { Plus, X, GripVertical } from "lucide-react";
@@ -70,15 +75,20 @@ export function AcceptanceCriteriaEditor({
                 onChange={(e) => handleUpdate(index, e.target.value)}
                 className="flex-1 h-8"
               />
-              <Button
-                type="button"
-                variant="ghost"
-                size="icon"
-                className="h-8 w-8 shrink-0"
-                onClick={() => handleRemove(index)}
-              >
-                <X className="h-4 w-4" />
-              </Button>
+              <Tooltip>
+                <TooltipTrigger asChild>
+                  <Button
+                    type="button"
+                    variant="ghost"
+                    size="icon"
+                    className="h-8 w-8 shrink-0"
+                    onClick={() => handleRemove(index)}
+                  >
+                    <X className="h-4 w-4" />
+                  </Button>
+                </TooltipTrigger>
+                <TooltipContent>Remove this criterion</TooltipContent>
+              </Tooltip>
             </div>
           ))}
         </div>