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/work-sessions/work-session-table.tsx

@@ -4,6 +4,11 @@ import { formatDistanceToNow } from "date-fns";
 import Link from "next/link";
 import { Badge } from "@/components/ui/badge";
 import { Button } from "@/components/ui/button";
+import {
+  Tooltip,
+  TooltipContent,
+  TooltipTrigger,
+} from "@/components/ui/tooltip";
 import {
   Table,
   TableBody,
@@ -147,14 +152,19 @@ export function WorkSessionTable({
                     })}
                   </TableCell>
                   <TableCell>
-                    <Link
-                      href={`/work-sessions/${session.id}`}
-                      prefetch={false}
-                    >
-                      <Button variant="ghost" size="icon">
-                        <ExternalLink className="h-4 w-4" />
-                      </Button>
-                    </Link>
+                    <Tooltip>
+                      <TooltipTrigger asChild>
+                        <Link
+                          href={`/work-sessions/${session.id}`}
+                          prefetch={false}
+                        >
+                          <Button variant="ghost" size="icon">
+                            <ExternalLink className="h-4 w-4" />
+                          </Button>
+                        </Link>
+                      </TooltipTrigger>
+                      <TooltipContent>Open work session</TooltipContent>
+                    </Tooltip>
                   </TableCell>
                 </TableRow>
               ))}
@@ -177,11 +187,19 @@ export function WorkSessionTable({
                     {session.branch_name}
                   </Link>
                 </div>
-                <Link href={`/work-sessions/${session.id}`} prefetch={false}>
-                  <Button variant="ghost" size="icon" className="shrink-0">
-                    <ExternalLink className="h-4 w-4" />
-                  </Button>
-                </Link>
+                <Tooltip>
+                  <TooltipTrigger asChild>
+                    <Link
+                      href={`/work-sessions/${session.id}`}
+                      prefetch={false}
+                    >
+                      <Button variant="ghost" size="icon" className="shrink-0">
+                        <ExternalLink className="h-4 w-4" />
+                      </Button>
+                    </Link>
+                  </TooltipTrigger>
+                  <TooltipContent>Open work session</TooltipContent>
+                </Tooltip>
               </div>
               <div className="mt-3 divide-y">
                 <ResponsiveTableCardRow label="Task">