Fix four defects the screenshots and tests exposed

Verifying the rendered pages rather than the build turned up real bugs:

- The WP-00 health page still sat at src/app/page.tsx and silently won
  the route over the new Aperçu screen, so the home page was a database
  status readout. Moved to /api/sante, where a probe belongs, and wired
  into the compose healthcheck.
- The unassigned row showed a +14 h delta against a contract of zero,
  reading as an overshoot when it is simply the volume left to staff.
  It now shows what there is to fill.
- Two sidebar entries lit at once: an anchor link matched its own page,
  and /equipe matched an employee record. Highlighting now resolves to
  the most specific match, and a test asserts exactly one entry lights
  per screen.
- Section tabs with no built screen pointed at the home page, which
  reads as a broken tab. They now lead to their first entry's
  placeholder.

Also gives truncated compliance alerts a title attribute, so a narrow
cell no longer says there is a problem without saying which.

Playwright can reuse a preinstalled browser through
PLAYWRIGHT_CHROMIUM_PATH when its revision differs from the bundled one.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Cr9dkEHwbDgkWPnyGj1Rjv

src/components/planning/CounterStrip.tsx

@@ -12,6 +12,8 @@ export interface CounterStripProps {
   counters: WeekCountersView;
   /** Vrai si le contrat est au forfait jours : pas de comparaison horaire. */
   forfaitJours?: boolean;
+  /** Ligne des besoins sans titulaire : il n'y a pas de contrat à comparer. */
+  unassigned?: boolean;
   className?: string;
 }
 
@@ -32,8 +34,23 @@ function Cell({ label, value }: { label: string; value: string }) {
 export function CounterStrip({
   counters,
   forfaitJours = false,
+  unassigned = false,
   className,
 }: CounterStripProps) {
+  // Un besoin non couvert n'a pas de contrat : afficher un écart le compare à
+  // zéro et fait lire « +14 h » comme un dépassement, alors que c'est
+  // simplement le volume à pourvoir.
+  if (unassigned) {
+    return (
+      <div className={cx('flex items-center gap-2 text-micro', className)}>
+        <span className="text-ink-3">À pourvoir</span>
+        <span className="tnum font-semibold text-ink-2">
+          {counters.plannedLabel}
+        </span>
+      </div>
+    );
+  }
+
   if (forfaitJours) {
     return (
       <div className={cx('flex items-center gap-2 text-micro', className)}>

src/components/planning/ShiftChip.tsx

@@ -87,7 +87,13 @@ export function ShiftChip({
       </span>
 
       {alert ? (
-        <span className="mt-px flex items-center gap-1 font-medium text-danger-soft-ink">
+        // Le motif est tronqué dans une cellule étroite : le `title` garde le
+        // texte complet accessible, sinon l'alerte dit qu'il y a un problème
+        // sans jamais dire lequel.
+        <span
+          className="mt-px flex items-center gap-1 font-medium text-danger-soft-ink"
+          title={alert}
+        >
           <span aria-hidden>▲</span>
           <span className="truncate">{alert}</span>
         </span>

src/components/planning/WeekGrid.tsx

@@ -106,6 +106,7 @@ function Row({ row, days }: { row: DemoWeekRow; days: readonly string[] }) {
         <CounterStrip
           counters={counters}
           forfaitJours={row.employee.forfaitJours ?? false}
+          unassigned={row.unassigned ?? false}
           className="mt-1"
         />
       </div>