feat(posts): images open the modal; only text expands in place

Post cards no longer expand the whole card on click (the old two-click path
to the images). The card is compact-only now:
- Hero / rail thumbs / the +N tile are buttons that open the post-scoped image
  modal (modal.open(id, { postImageIds })) so you view big + arrow through ALL
  the post's images. The feed caps thumbnails at 6, so for posts with more we
  lazily getPostFull to get the complete id list; +N opens at the first hidden
  image.
- The description is the ONLY in-place expansion: a Show more / Show less toggle
  shown only when the text is actually truncated (server description_truncated
  flag OR a measured CSS-clamp overflow, ResizeObserver-guarded). Expanding
  loads description_full when server-truncated and renders it unclamped.
- Attachments: download chips now render inline in the compact card (the feed
  already carries download_url), since the expanded view is gone.

Removes PostImageGrid.vue (the mosaic, now unused). Tests cover show-more
visibility + image-click opening the scoped modal.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/test/components/postCard.spec.js

@@ -1,26 +1,61 @@
 // @vitest-environment happy-dom
-import { describe, it, expect } from 'vitest'
+import { describe, it, expect, vi } from 'vitest'
+import { flushPromises } from '@vue/test-utils'
 
 import PostCard from '../../src/components/posts/PostCard.vue'
+import { useModalStore } from '../../src/stores/modal.js'
 import { freshPinia, mountComponent } from '../support/mountComponent.js'
 
+const now = new Date().toISOString()
+const BASE = {
+  id: 1, external_post_id: 'P1',
+  post_title: '<strong>Hello World</strong>',
+  post_url: 'https://x/1', post_date: now, downloaded_at: now,
+  artist: { id: 1, name: 'Sabu', slug: 'sabu' },
+  source: { id: 1, platform: 'subscribestar' },
+  thumbnails: [], thumbnails_more: 0, attachments: [],
+}
+
 describe('PostCard', () => {
   it('renders the HTML-stripped title and the artist', () => {
-    const pinia = freshPinia()
-    const now = new Date().toISOString()
-    const post = {
-      id: 1, external_post_id: 'P1',
-      post_title: '<strong>Hello World</strong>',
-      post_url: 'https://x/1', post_date: now, downloaded_at: now,
-      description_plain: 'a description',
-      artist: { id: 1, name: 'Sabu', slug: 'sabu' },
-      source: { id: 1, platform: 'subscribestar' },
-      thumbnails: [], thumbnails_more: 0, attachments: [],
-    }
-    const w = mountComponent(PostCard, { props: { post }, pinia })
+    const post = { ...BASE, description_plain: 'a description' }
+    const w = mountComponent(PostCard, { props: { post }, pinia: freshPinia() })
     const t = w.text()
     expect(t).toContain('Hello World')   // plain title
     expect(t).not.toContain('<strong>')  // tags stripped
     expect(t).toContain('Sabu')          // artist (RouterLink slot)
   })
+
+  it('shows a "Show more" toggle only when the description is truncated', () => {
+    const truncated = mountComponent(PostCard, {
+      props: { post: { ...BASE, description_plain: 'lots of text…', description_truncated: true } },
+      pinia: freshPinia(),
+    })
+    expect(truncated.text()).toContain('Show more')
+
+    const full = mountComponent(PostCard, {
+      props: { post: { ...BASE, description_plain: 'short', description_truncated: false } },
+      pinia: freshPinia(),
+    })
+    expect(full.text()).not.toContain('Show more')
+  })
+
+  it('clicking an image opens the post-scoped modal (never expands the card)', async () => {
+    const pinia = freshPinia()
+    const modal = useModalStore()
+    const openSpy = vi.spyOn(modal, 'open').mockResolvedValue()
+    const post = {
+      ...BASE,
+      description_plain: 'd',
+      thumbnails: [
+        { image_id: 10, thumbnail_url: '/a' },
+        { image_id: 11, thumbnail_url: '/b' },
+      ],
+      thumbnails_more: 0,
+    }
+    const w = mountComponent(PostCard, { props: { post }, pinia })
+    await w.find('.fc-post-card__hero').trigger('click')
+    await flushPromises()
+    expect(openSpy).toHaveBeenCalledWith(10, { postImageIds: [10, 11] })
+  })
 })