[Feat] (MG_Remote): the in-process display server serves unix endpoints too

mobilegl_server_serve_inprocess refused anything but tcp:// because its
only supervisor was the TCP one's thread hand-off. A unix endpoint
(@abstract name or filesystem path) now runs a supervisor of the same
shape minus the TCP exposure machinery: AcceptPair pairs a client's
control and SCM_RIGHTS connections by arrival order, there is no
DataBind to route and no pre-auth gate, sessions run on threads one at
a time with Busy for a second client, the latch resets between sessions
and g_inProcessStop ends it. That gives the on-screen server the
on-device fast path: ServerOwned windows over a unix socket with shm
data, no TCP copies.

The control screen's tcp-only guard for the on-screen mode goes with
the refusal it mirrored.

android-plugin/app/src/trace/java/top/mobilegl/plugin/ServerControlActivity.java

@@ -98,7 +98,7 @@ public final class ServerControlActivity extends Activity {
         envField = addField(contentLayout, "Extra env (optional)", "", dp(8));
 
         onScreenBox = new CheckBox(this);
-        onScreenBox.setText("On-screen window (render client frames onto this screen; tcp:// only)");
+        onScreenBox.setText("On-screen window (render client frames onto this screen)");
         onScreenBox.setTextColor(COLOR_TEXT);
         onScreenBox.setTextSize(TypedValue.COMPLEX_UNIT_SP, 13);
         LinearLayout.LayoutParams boxParams = new LinearLayout.LayoutParams(
@@ -155,14 +155,6 @@ public final class ServerControlActivity extends Activity {
         String token = tokenField.getText().toString();
         String env = envField.getText().toString().trim();
 
-        // The in-process display server only accepts tcp:// (ServerMain's in-process arm);
-        // the unix forms belong to the offscreen supervisor.
-        if (onScreenBox.isChecked() && !endpoint.startsWith("tcp://")) {
-            setStatus("The on-screen display server serves tcp:// only; use a tcp:// endpoint "
-                    + "or uncheck On-screen window.", COLOR_FAIL);
-            return;
-        }
-
         String probeDisplay;
         Probe probe;
         if (endpoint.startsWith("tcp://")) {