feat(plugins): seasonality + min-stay (Phase 3.2 + 3.4)

Plugin seasonality :
- Migration : Carbet.seasonalConstraints JSONB nullable
- lib/seasonality.ts : enum Season (DRY|LOW_WATER|WET), currentSeason() helper
  Guyane (juil-sept sèche, oct-nov étiage, déc-juin pluies), parseSeasonalConstraints,
  isCurrentlyOpen, SEASON_META (label/emoji/tone)
- Composant <SeasonBanner /> server, gated par plugin, ajouté dans layout
  au-dessus de tout le contenu — bandeau couleur+emoji+message contextuel

Plugin min-stay :
- Migration : Carbet.minStayNights, maxStayNights, minCapacity nullable
- Composant <StayConstraints /> client, gated par plugin — pill text
  '2 nuits minimum', '2-7 nuits', 'groupe 4+ recommandé'
- Carbet card et fiche enrichies avec les contraintes

Tous deux désactivables : sans le toggle, comportement legacy inchangé.

src/app/carbets/[slug]/page.tsx

@@ -16,6 +16,7 @@ import { CarbetGallery } from "../_components/carbet-gallery";
 import { ReviewsSection } from "../_components/reviews-section";
 import { StarRating } from "../_components/star-rating";
 import { AccessTypeBadge } from "@/components/AccessTypeBadge";
+import { StayConstraints } from "@/components/StayConstraints";
 
 type PageProps = {
   params: Promise<{ slug: string }>;
@@ -197,6 +198,18 @@ export default async function PublicCarbetPage({ params }: PageProps) {
                   {formatCoordinate(carbet.longitude)}
                 </dd>
               </div>
+              {(carbet.minStayNights || carbet.maxStayNights || carbet.minCapacity) ? (
+                <div>
+                  <dt className="font-medium text-zinc-500">Séjour</dt>
+                  <dd>
+                    <StayConstraints
+                      minNights={carbet.minStayNights}
+                      maxNights={carbet.maxStayNights}
+                      minCapacity={carbet.minCapacity}
+                    />
+                  </dd>
+                </div>
+              ) : null}
               <div>
                 <dt className="font-medium text-zinc-500">Capacité</dt>
                 <dd>

src/app/layout.tsx

@@ -3,6 +3,7 @@ import { Geist, Geist_Mono, Cormorant_Garamond } from "next/font/google";
 import "./globals.css";
 import { PluginProvider } from "@/lib/plugins/client";
 import { getEnabledPluginKeys, syncPluginsFromRegistry } from "@/lib/plugins/server";
+import { SeasonBanner } from "@/components/SeasonBanner";
 
 // Le layout interroge la DB Plugin à chaque request → rendu dynamique forcé.
 // Sans ça, le layout (et donc data-theme + enabledKeys passés au client) est
@@ -76,7 +77,10 @@ export default async function RootLayout({
         data-theme={themeGuyane ? "guyane" : undefined}
         className="min-h-full flex flex-col font-sans"
       >
-        <PluginProvider enabledKeys={enabledKeys}>{children}</PluginProvider>
+        <PluginProvider enabledKeys={enabledKeys}>
+          <SeasonBanner />
+          {children}
+        </PluginProvider>
       </body>
     </html>
   );