Phase 1: project scaffold, clap CLI, self-re-exec daemon, NDJSON IPC

- Cargo.toml with clap, tokio, serde, anyhow dependencies
- Entry point with env-var routing to daemon or CLI mode
- Core protocol types (Request/Response NDJSON wire format)
- Session detection (X11 check with DISPLAY/XDG_SESSION_TYPE)
- RefMap with @wN selector resolution (direct, prefix, substring)
- Snapshot/WindowInfo shared types with Display impl
- clap derive CLI with all subcommands (snapshot, click, type, etc.)
- Client connection: socket path resolution, daemon auto-start via
  self-re-exec, NDJSON send/receive with retry backoff
- Tokio async daemon: Unix socket listener, accept loop, graceful
  shutdown via notify
- DaemonState holding session info and ref map
- Placeholder handler returning hardcoded snapshot response

src/daemon/handler.rs

@@ -0,0 +1,31 @@
+use std::sync::Arc;
+use tokio::sync::Mutex;
+
+use crate::core::protocol::{Request, Response};
+use super::state::DaemonState;
+
+pub async fn handle_request(
+    request: &Request,
+    _state: &Arc<Mutex<DaemonState>>,
+) -> Response {
+    match request.action.as_str() {
+        "snapshot" => {
+            Response::ok(serde_json::json!({
+                "screenshot": "/tmp/desktop-ctl-placeholder.png",
+                "windows": [
+                    {
+                        "ref_id": "w1",
+                        "xcb_id": 0,
+                        "title": "Placeholder Window",
+                        "app_name": "placeholder",
+                        "x": 0, "y": 0, "width": 1920, "height": 1080,
+                        "focused": true, "minimized": false
+                    }
+                ]
+            }))
+        }
+        action => {
+            Response::err(format!("Unknown action: {action}"))
+        }
+    }
+}