feat(posts): plain bold titles; reserve View-original to the post card; provenance links to the posts feed

- Post titles arrived as stored HTML (e.g. <strong>…</strong>) rendering as
  literal markup. New toPlainText() strips tags; titles render plain + bold
  (ProvenancePanel and PostCard).
- Removed "View original post" from the provenance panel (modal) — the
  open-original button lives on the PostCard (the post view).
- Provenance "View post" now navigates to the /posts feed (post_id query),
  not the gallery image grid. (Feed in-context landing lands next.)

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

frontend/src/components/posts/PostCard.vue

@@ -56,8 +56,8 @@
       </div>
 
       <div class="fc-post-card__text">
-        <h3 v-if="post.post_title" class="fc-post-card__title">
-          {{ post.post_title }}
+        <h3 v-if="plainTitle" class="fc-post-card__title">
+          {{ plainTitle }}
         </h3>
         <h3 v-else class="fc-post-card__title fc-post-card__title--missing">
           Post {{ post.external_post_id }}
@@ -80,8 +80,8 @@
     <!-- Expanded body: title, full mosaic, full sanitized HTML description,
          attachments. Lazy-loaded detail via getPostFull. -->
     <div v-else class="fc-post-card__expanded">
-      <h2 v-if="post.post_title" class="fc-post-card__title-full">
-        {{ post.post_title }}
+      <h2 v-if="plainTitle" class="fc-post-card__title-full">
+        {{ plainTitle }}
       </h2>
       <h2 v-else class="fc-post-card__title-full fc-post-card__title--missing">
         Post {{ post.external_post_id }}
@@ -125,7 +125,7 @@ import { computed, ref } from 'vue'
 import { RouterLink } from 'vue-router'
 
 import { usePostsStore } from '../../stores/posts.js'
-import { sanitizeHtml } from '../../utils/htmlSanitize.js'
+import { sanitizeHtml, toPlainText } from '../../utils/htmlSanitize.js'
 import PostEmptyThumbs from './PostEmptyThumbs.vue'
 import PostImageGrid from './PostImageGrid.vue'
 
@@ -149,6 +149,10 @@ const merged = computed(() => detail.value || props.post)
 const images = computed(() => merged.value.thumbnails || [])
 const attachments = computed(() => merged.value.attachments || [])
 
+// Titles can arrive as stored HTML (e.g. "<strong>…</strong>"); render as
+// plain text — the CSS makes the title bold.
+const plainTitle = computed(() => toPlainText(props.post.post_title))
+
 // Compact-view hero+rail derived from the feed-shape (capped 6).
 const hero = computed(() => props.post.thumbnails?.[0])
 const rail = computed(() => (props.post.thumbnails || []).slice(1, 4))
@@ -312,7 +316,7 @@ function formatBytes (n) {
 
 .fc-post-card__title {
   font-family: 'Fraunces', Georgia, serif;
-  font-size: 18px; font-weight: 500;
+  font-size: 18px; font-weight: 700;
   margin: 0 0 8px 0;
   color: rgb(var(--v-theme-on-surface));
   display: -webkit-box;
@@ -369,7 +373,7 @@ function formatBytes (n) {
 .fc-post-card__title-full {
   font-family: 'Fraunces', Georgia, serif;
   font-size: 22px;
-  font-weight: 500;
+  font-weight: 700;
   margin: 0;
   color: rgb(var(--v-theme-on-surface));
 }