Add status column to context tree with tab-stop alignment

SectionView gains a status field for extra info displayed after the
token count column. Memory nodes section shows "N scored, M unscored"
in the status column instead of burying it in the title.

Renderer uses fixed-width columns (40 name, 16 tokens, status) for
consistent alignment across sections.

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

src/user/subconscious.rs

@@ -139,6 +139,7 @@ impl SubconsciousScreen {
                 tokens: 0,
                 content: val.clone(),
                 children: Vec::new(),
+                status: String::new(),
             }
         }).collect()
     }