poc-agent: read context_groups from config instead of hardcoded list

- Remove MEMORY_FILES constant from identity.rs
- Add ContextGroup struct for deserializing from config
- Load context_groups from ~/.config/poc-agent/config.json5
- Check ~/.config/poc-agent/ first for identity files, then project/global
- Debug screen now shows what's actually configured

This eliminates the hardcoded duplication and makes the debug output
match what's in the config file.

poc-agent/src/main.rs

@@ -843,11 +843,34 @@ impl Session {
         self.send_context_info();
     }
 
+    /// Load context_groups from the shared config file.
+    fn load_context_groups(&self) -> Vec<identity::ContextGroup> {
+        let config_path = dirs::home_dir()
+            .unwrap_or_else(|| PathBuf::from("."))
+            .join(".config/poc-agent/config.json5");
+        
+        if let Ok(content) = std::fs::read_to_string(&config_path) {
+            let config: Result<serde_json::Value, _> = json5::from_str(&content);
+            if let Ok(config) = config {
+                if let Some(memory) = config.get("memory") {
+                    if let Some(groups) = memory.get("context_groups") {
+                        if let Ok(context_groups) = serde_json::from_value(groups.clone()) {
+                            return context_groups;
+                        }
+                    }
+                }
+            }
+        }
+        Vec::new()
+    }
+
     /// Send context loading info to the TUI debug screen.
     fn send_context_info(&self) {
+        let context_groups = self.load_context_groups();
         let (instruction_files, memory_files) = identity::context_file_info(
             &self.config.prompt_file,
             self.config.app.memory_project.as_deref(),
+            &context_groups,
         );
         let _ = self.ui_tx.send(UiMessage::ContextInfoUpdate(ContextInfo {
             model: self.config.model.clone(),