fix: unconscious agent cycling

- Read max_concurrent from config (llm_concurrency) instead of hardcoding 2
- Add not-visited: and visited: filters to query parser (were in engine
  but missing from parser after unification)

The organize agent was stuck in a spawn/fail loop because its query used
not-visited: which the parser didn't recognize.

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

src/mind/unconscious.rs

@@ -111,8 +111,10 @@ impl Unconscious {
         }
         agents.sort_by(|a, b| a.name.cmp(&b.name));
 
+        let max_concurrent = crate::config::get().llm_concurrency;
+
         Self {
-            agents, max_concurrent: 2,
+            agents, max_concurrent,
             graph_health: None,
             last_health_check: None,
         }