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-memory/src/store/ops.rs

@@ -7,11 +7,18 @@ use super::types::*;
 
 use std::collections::{HashMap, HashSet};
 
-/// Provenance from POC_PROVENANCE env var, defaulting to "manual".
+tokio::task_local! {
+    /// Task-scoped provenance for agent writes. Set by the daemon before
+    /// running an agent's tool calls, so all writes within that task are
+    /// automatically attributed to the agent.
+    pub static TASK_PROVENANCE: String;
+}
+
+/// Provenance priority: task_local (agent context) > env var > "manual".
 fn current_provenance() -> String {
-    Provenance::from_env()
-        .map(|p| p.label().to_string())
-        .unwrap_or_else(|| "manual".to_string())
+    TASK_PROVENANCE.try_with(|p| p.clone())
+        .or_else(|_| std::env::var("POC_PROVENANCE").map_err(|_| ()))
+        .unwrap_or_else(|_| "manual".to_string())
 }
 
 impl Store {