feat(post-card): absorb PostModal into PostCard with click-to-expand

PostCard and PostModal competed for the same data and rendered redundant
chrome (header twice, image grid twice, attachment list twice). The wider
PostCard layout we shipped 2026-05-27 has enough real estate to be the
canonical post surface, so collapse the two into one.

Compact (default) state is unchanged: hero + 3-cell rail + truncated
title + 3/5-line description + attachment count badge. Whole-card click
expands in place. Expanded state shows: full title, mosaic of ALL post
images via PostImageGrid (uncapped, lazy-loaded via getPostFull), full
sanitized-HTML description with paragraph wrapping, attachments as
downloadable pill links. Click the chevron in the header to collapse;
mosaic image clicks open ImageViewer scoped to the post (modalStore's
postImageIds path is preserved — only the comment changed).

Per-card local state — no global modal store. Each PostCard owns its
own expanded ref and lazy-loaded detail; collapsing a card discards
neither (so re-expand is instant after the first fetch).

Deleted: PostModal.vue, postModal.js store. Removed the App.vue mount.

frontend/src/stores/modal.js

@@ -11,9 +11,9 @@ export const useModalStore = defineStore('modal', () => {
   const error = ref(null)
 
   // Post-scoped cycle. When set, prev/next cycles within this array
-  // (used by PostModal's PostImageGrid clicks). When null, prev/next
-  // falls back to current.value.neighbors (the gallery-store-driven
-  // /api/gallery/image/<id> neighbors).
+  // (used by PostCard's expanded-mosaic PostImageGrid clicks). When
+  // null, prev/next falls back to current.value.neighbors (the
+  // gallery-store-driven /api/gallery/image/<id> neighbors).
   const postImageIds = ref(null)
   const postImageIndex = ref(0)
 

frontend/src/stores/postModal.js

@@ -1,39 +0,0 @@
-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 }
-})