Logo annuaire + modals devenir membre & contact

- Logo en haut a gauche de la page Annuaire (prop logo sur SiteHeader)
- Modal "Devenir adherent" sur les CTA accueil + annuaire : cree une
  demande d'adhesion (membership_requests) et alerte les admins via le
  journal d'activite (compteur tableau de bord deja cable)
- Formulaire de contact (modal depuis le pied de page) : nouvelle table
  contact_messages + alerte admin
- Composant Modal partage, server actions publiques (sans auth)
- Migration drizzle 0002

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/SiteHeader.tsx

@@ -7,18 +7,24 @@ const NAV = [
   { key: "association", label: "L'association", href: "#" },
 ];
 
-export function SiteHeader({ active }: { active?: string }) {
+export function SiteHeader({ active, logo = false }: { active?: string; logo?: boolean }) {
   return (
     <header
       className="container"
       style={{
         display: "flex",
         alignItems: "center",
-        justifyContent: "flex-end",
+        justifyContent: logo ? "space-between" : "flex-end",
         padding: "18px 56px",
         gap: 20,
       }}
     >
+      {logo && (
+        <Link href="/" aria-label="Plein R — accueil" style={{ display: "inline-flex", alignItems: "center" }}>
+          {/* eslint-disable-next-line @next/next/no-img-element */}
+          <img src="/assets/logo.png" alt="Plein R" style={{ height: 46, width: "auto", display: "block" }} />
+        </Link>
+      )}
       <nav style={{ display: "flex", alignItems: "center", gap: 30, flexWrap: "wrap" }}>
         {NAV.map((n) => {
           const isActive = active === n.key;