feat(postmodal-store): Pinia store driving the app-level PostModal — open(post) fetches full detail via posts store; close() clears

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/stores/postModal.js

@@ -0,0 +1,39 @@
+import { defineStore } from 'pinia'
+import { ref, computed } from 'vue'
+import { usePostsStore } from './posts.js'
+
+export const usePostModalStore = defineStore('postModal', () => {
+  const postsStore = usePostsStore()
+
+  // Feed-shape on open; upgraded to detail shape (full description +
+  // uncapped thumbnails) once getPostFull resolves.
+  const currentPost = ref(null)
+  const detailLoaded = ref(false)
+  const error = ref(null)
+  const isOpen = computed(() => currentPost.value !== null)
+
+  async function open (post) {
+    currentPost.value = post
+    detailLoaded.value = false
+    error.value = null
+    try {
+      const detail = await postsStore.getPostFull(post.id)
+      if (currentPost.value?.id === post.id) {
+        currentPost.value = detail
+        detailLoaded.value = true
+      }
+    } catch (e) {
+      // Keep feed-shape data; PostModal can still render title + truncated
+      // description + the up-to-6 feed thumbnails. Just surface the error.
+      error.value = e.message
+    }
+  }
+
+  function close () {
+    currentPost.value = null
+    detailLoaded.value = false
+    error.value = null
+  }
+
+  return { currentPost, detailLoaded, error, isOpen, open, close }
+})