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/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>