fix: prevent daemon silent death from SIGHUP + unhandled errors

Root cause: registerSignalHandlers() handled SIGTERM/SIGINT but not
SIGHUP. When the parent hook process exits, the kernel sends SIGHUP
to the daemon, causing immediate termination (default signal action).

Belt-and-suspenders fix:
1. SIGHUP handler: ignore in daemon mode, graceful shutdown otherwise
2. setsid: spawn daemon in new session on Linux (prevents SIGHUP delivery)
3. Global unhandledRejection/uncaughtException guards in daemon mode

src/services/infrastructure/ProcessManager.ts

@@ -384,7 +384,27 @@ export function spawnDaemon(
     }
   }
 
-  // Unix: standard detached spawn
+  // Unix: Use setsid to create a new session, fully detaching from the
+  // controlling terminal. This prevents SIGHUP from reaching the daemon
+  // even if the in-process SIGHUP handler somehow fails (belt-and-suspenders).
+  // Fall back to standard detached spawn if setsid is not available.
+  const setsidPath = '/usr/bin/setsid';
+  if (existsSync(setsidPath)) {
+    const child = spawn(setsidPath, [process.execPath, scriptPath, '--daemon'], {
+      detached: true,
+      stdio: 'ignore',
+      env
+    });
+
+    if (child.pid === undefined) {
+      return undefined;
+    }
+
+    child.unref();
+    return child.pid;
+  }
+
+  // Fallback: standard detached spawn (macOS, systems without setsid)
   const child = spawn(process.execPath, [scriptPath, '--daemon'], {
     detached: true,
     stdio: 'ignore',