refactor: apply newtypes throughout userspace API and display types

Every syscall stub now uses proper types from types/ — CapSlot,
EntryPoint, StackPointer, VirtualAddress, PageCount, ProcessId,
PermissionSet, Ticks. The compiler prevents swapping entry/stack,
passing a ProcessId where a CapSlot is expected, or using an
address as a page count.

New display types in types/display.rs:
  - Color(u32) with rgb() constructor
  - ScreenCoord(u16) for x/y positions
  - Dimension(u16) for width/height

Updated throughout:
  - userspace/syscall.rs: all params typed, returns Option instead
    of sentinel usize::MAX
  - server-framework: endpoint param is CapSlot
  - port-framebuffer: trait uses Color, ScreenCoord, Dimension
  - hw-virtio: DmaAddrs uses PhysicalAddress/VirtualAddress,
    GPU commands use Dimension
  - All servers, drivers, bins, apps updated for new signatures
  - permission-manager: process field uses ProcessId
  - PermissionSet: added bits() accessor

89 tests pass, full QEMU boot verified.

crates/servers/display-server/src/protocol.rs

@@ -1,9 +1,10 @@
 use server_framework::{Decode, Encode};
+use types::display::{Color, Dimension, ScreenCoord};
 
 #[derive(Debug, PartialEq)]
 pub enum DisplayRequest {
-    DrawRect { x: u16, y: u16, w: u16, h: u16, color: u32 },
-    Clear { color: u32 },
+    DrawRect { x: ScreenCoord, y: ScreenCoord, w: Dimension, h: Dimension, color: Color },
+    Clear { color: Color },
     Flush,
     GetDimensions,
 }
@@ -11,7 +12,7 @@ pub enum DisplayRequest {
 #[derive(Debug, PartialEq)]
 pub enum DisplayResponse {
     Ok,
-    Dimensions { width: u16, height: u16 },
+    Dimensions { width: Dimension, height: Dimension },
     Error,
 }
 
@@ -19,11 +20,11 @@ impl Encode for DisplayRequest {
     fn encode(&self) -> [usize; 4] {
         match self {
             DisplayRequest::DrawRect { x, y, w, h, color } => {
-                let xy = (*x as usize) | ((*y as usize) << 16);
-                let wh = (*w as usize) | ((*h as usize) << 16);
-                [0, xy, wh, *color as usize]
+                let xy = (x.raw() as usize) | ((y.raw() as usize) << 16);
+                let wh = (w.raw() as usize) | ((h.raw() as usize) << 16);
+                [0, xy, wh, color.raw() as usize]
             }
-            DisplayRequest::Clear { color } => [1, *color as usize, 0, 0],
+            DisplayRequest::Clear { color } => [1, color.raw() as usize, 0, 0],
             DisplayRequest::Flush => [2, 0, 0, 0],
             DisplayRequest::GetDimensions => [3, 0, 0, 0],
         }
@@ -34,14 +35,14 @@ impl Decode for DisplayRequest {
     fn decode(words: [usize; 4]) -> Option<Self> {
         match words[0] {
             0 => {
-                let x = (words[1] & 0xFFFF) as u16;
-                let y = ((words[1] >> 16) & 0xFFFF) as u16;
-                let w = (words[2] & 0xFFFF) as u16;
-                let h = ((words[2] >> 16) & 0xFFFF) as u16;
-                let color = words[3] as u32;
+                let x = ScreenCoord::new((words[1] & 0xFFFF) as u16);
+                let y = ScreenCoord::new(((words[1] >> 16) & 0xFFFF) as u16);
+                let w = Dimension::new((words[2] & 0xFFFF) as u16);
+                let h = Dimension::new(((words[2] >> 16) & 0xFFFF) as u16);
+                let color = Color::from_raw(words[3] as u32);
                 Some(DisplayRequest::DrawRect { x, y, w, h, color })
             }
-            1 => Some(DisplayRequest::Clear { color: words[1] as u32 }),
+            1 => Some(DisplayRequest::Clear { color: Color::from_raw(words[1] as u32) }),
             2 => Some(DisplayRequest::Flush),
             3 => Some(DisplayRequest::GetDimensions),
             _ => None,
@@ -54,7 +55,7 @@ impl Encode for DisplayResponse {
         match self {
             DisplayResponse::Ok => [0, 0, 0, 0],
             DisplayResponse::Dimensions { width, height } => {
-                [1, *width as usize, *height as usize, 0]
+                [1, width.raw() as usize, height.raw() as usize, 0]
             }
             DisplayResponse::Error => [2, 0, 0, 0],
         }
@@ -66,8 +67,8 @@ impl Decode for DisplayResponse {
         match words[0] {
             0 => Some(DisplayResponse::Ok),
             1 => Some(DisplayResponse::Dimensions {
-                width: words[1] as u16,
-                height: words[2] as u16,
+                width: Dimension::new(words[1] as u16),
+                height: Dimension::new(words[2] as u16),
             }),
             2 => Some(DisplayResponse::Error),
             _ => None,