feat: controller/gamepad support (#350)

Adds `nesgamepad`, basically "diet-coke vimputti" for Nestri's microVM
needs here.

Comes with direct mapping for:
- Sony
  - DualShock 4 (v2), DualSense
- Microsoft
  - Xbox 360 pad, Xbox One S pad
- Nintendo
  - Pro Controller
- Generic pad for unknown controllers

---------

Co-authored-by: DatCaptainHorse <DatCaptainHorse@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

apps/nesinit/src/services.rs

@@ -221,7 +221,8 @@ const WRITABLE: &[(&str, &str)] = &[
 ///
 /// Ported from the nine init scripts this replaces, and the ordering is theirs:
 /// the bus before anything that speaks on it, audio before whatever plays into
-/// it, and the hub last because it binds the sockets the rest connect to.
+/// it, and the hub after them because it binds the sockets the rest connect to.
+/// Only something that dials the hub, and waits for it, comes after.
 pub const STACK: &[Service] = &[
     Service {
         name: "dbus-system",
@@ -337,6 +338,23 @@ pub const STACK: &[Service] = &[
         umask: None,
         ready: None,
     },
+    Service {
+        name: "nesgamepad",
+        argv: &["/usr/bin/nesgamepad"],
+        env: &[],
+        // Root, and it has to be: it creates devices through /dev/uinput,
+        // opens their nodes to the workload, and announces them the way udev
+        // would -- and libudev ignores an announcement from anyone but root.
+        user: None,
+        // Optional: a session without controllers is still played with a
+        // keyboard and mouse.
+        cost: "controllers plugged into the client do not reach the game",
+        required: false,
+        umask: None,
+        // It dials the hub rather than the other way round, and redials until
+        // the hub is there, so nothing waits on it.
+        ready: None,
+    },
 ];
 
 /// The stack as running processes.

apps/nesinit/src/system.rs

@@ -13,6 +13,10 @@
 // compositor handles input through Wayland and opens nothing udev provides, so
 // dropping it costs a box nothing and saves it a daemon and a settle.
 //
+// The one thing in a box that does need udev is a game looking for
+// controllers, and those are devices `nesgamepad` creates itself -- so it
+// stands in for udev for exactly those, and nothing else has to.
+//
 // # Best effort, one line per failure, each naming a cost
 //
 // Same discipline as the early filesystems: refusing to boot over any one of