split into workspace: poc-memory and poc-daemon subcrates

poc-daemon (notification routing, idle timer, IRC, Telegram) was already
fully self-contained with no imports from the poc-memory library. Now it's
a proper separate crate with its own Cargo.toml and capnp schema.

poc-memory retains the store, graph, search, neuro, knowledge, and the
jobkit-based memory maintenance daemon (daemon.rs).

Co-Authored-By: ProofOfConcept <poc@bcachefs.org>

poc-memory/src/util.rs

@@ -0,0 +1,14 @@
+// Shared utilities
+
+use crate::store;
+
+use std::fs;
+use std::path::PathBuf;
+
+/// Ensure a subdirectory of the memory dir exists and return its path.
+pub fn memory_subdir(name: &str) -> Result<PathBuf, String> {
+    let dir = store::memory_dir().join(name);
+    fs::create_dir_all(&dir)
+        .map_err(|e| format!("create {}: {}", dir.display(), e))?;
+    Ok(dir)
+}