Replace push() with explicit push_log() and push_no_log()

No implicit auto-logging. Call sites choose:
- push_log: new conversation entries (user messages, tool results,
  surfaced memories, assistant responses)
- push_no_log: system prompt, identity, journal, restore from log,
  compact reload, tests

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/mind/subconscious.rs

@@ -541,7 +541,7 @@ impl Subconscious {
         if !nodes.is_empty() {
             let mut ctx = agent.context.lock().await;
             for node in nodes {
-                ctx.push(Section::Conversation, node);
+                ctx.push_log(Section::Conversation, node);
             }
             drop(ctx);
             agent.state.lock().await.changed.notify_one();