extract jobkit-daemon library from poc-memory daemon

Create jobkit-daemon crate with generic daemon infrastructure:
- event_log: JSONL append with size-based rotation
- socket: Unix domain socket RPC client and server with signal handling
- status: JSON status file read/write

Migrate daemon.rs to use the library:
- Worker pool setup via Daemon::new()
- Socket loop + signal handling via Daemon::run()
- RPC handlers as registered closures
- Logging, status writing, send_rpc all delegate to library

Migrate tui.rs to use socket::send_rpc() instead of inline UnixStream.

daemon.rs: 1952 → 1806 lines (-146), old status_socket_loop removed.
tui.rs: socket boilerplate removed.

Co-Authored-By: Kent Overstreet <kent.overstreet@linux.dev>

jobkit-daemon/src/status.rs

@@ -0,0 +1,29 @@
+// Status file management
+//
+// Writes a JSON status snapshot to data_dir/daemon-status.json.
+// Applications provide their own status struct (must impl Serialize).
+
+use std::fs;
+use std::path::Path;
+
+fn status_path(data_dir: &Path) -> std::path::PathBuf {
+    data_dir.join("daemon-status.json")
+}
+
+/// Write a status snapshot to the status file.
+pub fn write<S: serde::Serialize>(data_dir: &Path, status: &S) {
+    if let Ok(json) = serde_json::to_string_pretty(status) {
+        let _ = fs::write(status_path(data_dir), json);
+    }
+}
+
+/// Read the status file as a string.
+pub fn read(data_dir: &Path) -> Option<String> {
+    fs::read_to_string(status_path(data_dir)).ok()
+}
+
+/// Read and deserialize the status file.
+pub fn load<S: serde::de::DeserializeOwned>(data_dir: &Path) -> Option<S> {
+    let s = read(data_dir)?;
+    serde_json::from_str(&s).ok()
+}