feat: PC5 col D embeds Insta via Behold (avec fallback profil statique)

- InstaFeed.vue (Vue island) : consomme feeds.behold.so/{feedId}, skeleton loading, grid 2x3 thumbnails, fallback profil si placeholder ou erreur
- ColInsta.astro enrichi : 2 sections @aep.politique + @julesneny, hydratation client:visible (lazy)
- .env.example committe (PUBLIC_BEHOLD_AEP/JULESNENY vides) ; .env.local deja gitignore
- docs/BEHOLD-SETUP.md : procedure inscription + recup feed IDs + alternatives + note CSP PC8

Action Jules requise (async) : inscription Behold + connexion 2 comptes Insta + remplir .env.local.

src/components/astro/ColInsta.astro

@@ -1,12 +1,24 @@
 ---
-// Placeholder Insta : 2 carrousels @aep + @julesneny — PC5 oEmbed
+import InstaFeed from '../vue/InstaFeed.vue';
+
+// Feed IDs Behold a remplir apres inscription Behold (voir docs/BEHOLD-SETUP.md)
+const FEED_AEP = import.meta.env.PUBLIC_BEHOLD_AEP || 'PLACEHOLDER_AEP';
+const FEED_JULESNENY = import.meta.env.PUBLIC_BEHOLD_JULESNENY || 'PLACEHOLDER_JULESNENY';
 ---
-<section class="h-full p-4 flex flex-col gap-4">
-  <h2 class="text-lg font-semibold text-neutral-700">Insta</h2>
-  <div class="border border-dashed border-neutral-300 rounded p-3 flex-1 flex items-center justify-center">
-    <p class="text-sm text-neutral-400">@aep carrousel — PC5</p>
-  </div>
-  <div class="border border-dashed border-neutral-300 rounded p-3 flex-1 flex items-center justify-center">
-    <p class="text-sm text-neutral-400">@julesneny carrousel — PC5</p>
-  </div>
-</section>
+<div class="h-full overflow-y-auto">
+  <InstaFeed
+    client:visible
+    feedId={FEED_AEP}
+    account="@aep.politique"
+    accountUrl="https://www.instagram.com/aep.politique/"
+    fallbackBio="Carrousels manifeste AEP ; pensee politique eco-architecture"
+  />
+
+  <InstaFeed
+    client:visible
+    feedId={FEED_JULESNENY}
+    account="@julesneny"
+    accountUrl="https://www.instagram.com/julesneny/"
+    fallbackBio="Peinture, poesie, Corse ; archives visuelles personnelles"
+  />
+</div>