Cross-platform IPC via interprocess + Windows support fixes

- Replace Unix-socket-only server/client with interprocess local sockets:
  unchanged unix domain socket on Linux (SOCKET_API compatible),
  named pipes on Windows
- Run command lines with arguments via sh -c / cmd /C in the PTY
- Wire RunProgram args into the spawned command
- Make libc a unix-only dependency
- Skip Kitty background image on Windows (protocol unsupported)
- Drop dead pixel-size query code in kitty_gfx
- Reject left/right panel positions at config parse instead of silently
  ignoring them

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/server.rs

@@ -1,6 +1,7 @@
 use crate::ipc::{self, ClientMessage, ClientRole, ServerMessage};
+use interprocess::local_socket::traits::{ListenerExt as _, Stream as _};
+use interprocess::local_socket::{ListenerOptions, Stream};
 use std::io::{BufReader, BufWriter};
-use std::os::unix::net::{UnixListener, UnixStream};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::sync::mpsc;
 use std::thread;
@@ -25,11 +26,21 @@ pub enum IpcEvent {
 }
 
 pub fn start(socket_path: &str, event_tx: mpsc::Sender<IpcEvent>) {
+    // På unix: städa bort en ev. kvarlämnad socket-fil från en tidigare körning.
+    #[cfg(unix)]
     let _ = std::fs::remove_file(socket_path);
-    let listener = match UnixListener::bind(socket_path) {
+
+    let name = match ipc::socket_name(socket_path) {
+        Ok(n) => n,
+        Err(e) => {
+            eprintln!("Ogiltigt socket-namn {}: {}", socket_path, e);
+            return;
+        }
+    };
+    let listener = match ListenerOptions::new().name(name).create_sync() {
         Ok(l) => l,
         Err(e) => {
-            eprintln!("Kunde inte binda Unix socket {}: {}", socket_path, e);
+            eprintln!("Kunde inte binda lokal socket {}: {}", socket_path, e);
             return;
         }
     };
@@ -45,7 +56,8 @@ pub fn start(socket_path: &str, event_tx: mpsc::Sender<IpcEvent>) {
                         handle_client(client_id, stream, event_tx, sp);
                     });
                 }
-                Err(_) => break,
+                // Transienta accept-fel (kan hända för named pipes) — fortsätt lyssna.
+                Err(_) => continue,
             }
         }
     });
@@ -53,20 +65,17 @@ pub fn start(socket_path: &str, event_tx: mpsc::Sender<IpcEvent>) {
 
 fn handle_client(
     client_id: usize,
-    stream: UnixStream,
+    stream: Stream,
     event_tx: mpsc::Sender<IpcEvent>,
     socket_path: String,
 ) {
-    let stream_write = match stream.try_clone() {
-        Ok(s) => s,
-        Err(_) => return,
-    };
-    let mut reader = BufReader::new(stream);
+    let (recv_half, send_half) = stream.split();
+    let mut reader = BufReader::new(recv_half);
     let (tx, rx) = mpsc::sync_channel::<ServerMessage>(64);
 
     // Writer thread
     thread::spawn(move || {
-        let mut writer = BufWriter::new(stream_write);
+        let mut writer = BufWriter::new(send_half);
         for msg in rx {
             if ipc::write_message(&mut writer, &msg).is_err() {
                 break;