Use full post body in AP notes, not just excerpt

Federated content has no character limit — use the complete plaintext
body so followers see the full post in their timeline.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bp/blog/ghost/ghost_sync.py

@@ -1006,14 +1006,10 @@ def _build_ap_post_data(post, post_url: str, tag_objs: list) -> dict:
     if post.title:
         parts.append(f"<p>{html_escape(post.title)}</p>")
 
-    excerpt = post.custom_excerpt or post.excerpt or ""
-    if not excerpt and post.plaintext:
-        excerpt = post.plaintext[:500]
-        if len(post.plaintext) > 500:
-            excerpt = excerpt.rsplit(" ", 1)[0] + "\u2026"
+    body = post.plaintext or post.custom_excerpt or post.excerpt or ""
 
-    if excerpt:
-        for para in excerpt.split("\n\n"):
+    if body:
+        for para in body.split("\n\n"):
             para = para.strip()
             if para:
                 parts.append(f"<p>{html_escape(para)}</p>")