Spacebar toggle for all agents, persist to config, scan agent directory

- Scan agents directory for all .agent files instead of hardcoded list
- Persist enabled state to ~/.consciousness/agent-enabled.json
- Spacebar on F3 agent list toggles selected agent on/off
- Both subconscious and unconscious agents support toggle
- Disabled agents shown dimmed with "off" indicator
- New agents default to disabled (safe default)

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

src/mind/subconscious.rs

@@ -439,6 +439,13 @@ impl Subconscious {
         }
     }
 
+    /// Toggle an agent on/off by name. Returns new enabled state.
+    pub fn toggle(&mut self, name: &str) -> Option<bool> {
+        let agent = self.agents.iter_mut().find(|a| a.name == name)?;
+        agent.auto.enabled = !agent.auto.enabled;
+        Some(agent.auto.enabled)
+    }
+
     pub fn walked(&self) -> Vec<String> {
         self.state.get("walked")
             .map(|s| s.lines().map(|l| l.trim().to_string()).filter(|l| !l.is_empty()).collect())