Phase 1 (0.6.0-beta): remove direct PostPush for encrypted posts

Encrypted posts now propagate only via the CDN (ManifestPush + neighbor
header updates), eliminating the sender→recipient traffic signal on the
wire. Encrypted DMs are indistinguishable from any other encrypted post.

- Remove push_post_to_recipients entirely from network.rs
- Remove call sites in create_post and re-encrypt-on-revoke
- PostPush handler now ignores non-public visibility (kept for public
  audience push path)

Known gap: non-follower DMs won't reach until Phase 3 (merged pull +
recipient-match). Followers receive via the existing CDN path — new
posts trigger neighbor-manifest updates, ManifestPush fans out to
downstream holders, recipients pull missing post IDs from followed
authors.

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

crates/core/src/network.rs

@@ -902,50 +902,6 @@ impl Network {
         self.send_to_audience(MessageType::PostNotification, &payload).await
     }
 
-    /// Push a full post directly to recipients (persistent if available, ephemeral otherwise).
-    pub async fn push_post_to_recipients(
-        &self,
-        post_id: &crate::types::PostId,
-        post: &Post,
-        visibility: &PostVisibility,
-    ) -> usize {
-        let recipients: Vec<NodeId> = match visibility {
-            PostVisibility::Public => return 0,
-            PostVisibility::Encrypted { recipients } => {
-                recipients.iter().map(|wk| wk.recipient).collect()
-            }
-            PostVisibility::GroupEncrypted { group_id, .. } => {
-                // Push to all group members
-                match self.storage.get().await.get_all_group_members() {
-                    Ok(map) => map.get(group_id).cloned().unwrap_or_default().into_iter().collect(),
-                    Err(_) => return 0,
-                }
-            }
-        };
-
-        let payload = PostPushPayload {
-            post: SyncPost {
-                id: *post_id,
-                post: post.clone(),
-                visibility: visibility.clone(),
-            },
-        };
-
-        let mut pushed = 0;
-        for recipient in &recipients {
-            if self.send_to_peer_uni(recipient, MessageType::PostPush, &payload).await.is_ok() {
-                pushed += 1;
-                debug!(
-                    recipient = hex::encode(recipient),
-                    post_id = hex::encode(post_id),
-                    "Pushed post to recipient"
-                );
-            }
-        }
-
-        pushed
-    }
-
     /// Push a profile update to all audience members (ephemeral-capable).
     pub async fn push_profile(&self, profile: &PublicProfile) -> usize {
         // Sanitize: if public_visible=false, strip display_name/bio from pushed profile