daemon: use CLAUDE_CONFIG_DIR for OAuth credential separation, fix shutdown

Replace agent_api_key (which didn't work — claude CLI uses OAuth, not
API keys) with agent_config_dir. When configured, sets CLAUDE_CONFIG_DIR
on claude subprocesses so daemon agent work authenticates with separate
OAuth credentials from the interactive session.

Fix daemon not shutting down on SIGTERM: use process::exit(0) after
cleanup so PR_SET_PDEATHSIG kills child claude processes immediately.
Previously the daemon hung waiting for choir threads/subprocesses to
finish. Restart now takes ~20ms instead of timing out.

Also: main.rs now uses `use poc_memory::*` since lib.rs exists.

src/daemon.rs

@@ -487,18 +487,14 @@ pub fn run_daemon() -> Result<(), String> {
     log_event("daemon", "stopping", "");
     eprintln!("Shutting down...");
 
-    // Cancel all tasks
-    for info in choir_main.task_statuses() {
-        if !info.status.is_finished() {
-            log_event(&info.name, "cancelling", "");
-        }
-    }
-
     // Clean up socket
     let _ = fs::remove_file(status_sock_path());
 
     log_event("daemon", "stopped", "");
-    Ok(())
+
+    // Exit immediately — PR_SET_PDEATHSIG on child processes ensures
+    // claude subprocesses get SIGTERM when we die.
+    std::process::exit(0)
 }
 
 fn read_status_socket() -> Option<DaemonStatus> {