restructure: rsnix kernel + shell crate + rsdos entry point

Architecture:
  rs-dos/  (workspace root, was raisernics/)
  ├── rsnix/     — kernel lib crate (uefi, serial, gop, ps2, interrupts, memory)
  ├── shell/     — shell lib crate (prompt, commands, line input)
  ├── rsdos/     — binary crate (efi_main, init, panic handler)
  └── rsboot/    — future git submodule

No functional changes — boots to shell prompt identically.
Version auto-pulled from Cargo.toml via env!("CARGO_PKG_VERSION").

10 files changed, 20 insertions, 6 deletions

diff --git a/rsnix/Cargo.toml b/rsnix/Cargo.toml
new file mode 100644
index 0000000..d8cd26b
--- /dev/null
+++ b/rsnix/Cargo.toml
@@ -0,0 +1,4 @@
+[package]
+name = "rsnix"
+version.workspace = true
+edition.workspace = true
diff --git a/build.rs b/rsnix/build.rs
index 35447e9..35447e9 100644
--- a/build.rs
+++ b/rsnix/build.rs
diff --git a/src/font.rs b/rsnix/src/font.rs
index e188513..e188513 100644
--- a/src/font.rs
+++ b/rsnix/src/font.rs
diff --git a/src/gop.rs b/rsnix/src/gop.rs
index 9645bb0..9645bb0 100644
--- a/src/gop.rs
+++ b/rsnix/src/gop.rs
diff --git a/src/interrupts.rs b/rsnix/src/interrupts.rs
index 90d5bbb..8f2acd7 100644
--- a/src/interrupts.rs
+++ b/rsnix/src/interrupts.rs
@@ -174,7 +174,7 @@ impl KeyBuf {
         let h = self.head.load(Ordering::Acquire);
         let next = t.wrapping_add(1);
         // Full if the distance between head and tail == capacity (256).
-        if next.wrapping_sub(h) as u16 > 255 {
+        if next.wrapping_sub(h) > 255 {
             return; // drop — ring is full
         }
         unsafe {
@@ -362,7 +362,7 @@ pub fn init() {
 
         // Build the IDTR pseudo-descriptor.
         IDTR = [
-            (256u16 * 16 - 1) as u16,      // limit = 256*16 - 1
+            ((256u16 * 16 - 1)),      // limit = 256*16 - 1
             idt_ptr as u16,                // base lo
             (idt_ptr as u64 >> 16) as u16, // base mid
             (idt_ptr as u64 >> 32) as u16, // base hi
diff --git a/rsnix/src/lib.rs b/rsnix/src/lib.rs
new file mode 100644
index 0000000..6c7fb3c
--- /dev/null
+++ b/rsnix/src/lib.rs
@@ -0,0 +1,11 @@
+#![no_std]
+
+extern crate alloc;
+
+pub mod uefi;
+pub mod serial;
+pub mod gop;
+pub mod font;
+pub mod ps2;
+pub mod interrupts;
+pub mod memory;
diff --git a/src/memory.rs b/rsnix/src/memory.rs
index d223f69..39fd88d 100644
--- a/src/memory.rs
+++ b/rsnix/src/memory.rs
@@ -85,7 +85,7 @@ pub fn capture_memory_map(bs: &BootServices) -> Result<usize, Status> {
     }
 
     // Round up to desc_size alignment
-    let buf_size = (buf_size + desc_size - 1) / desc_size * desc_size;
+    let buf_size = buf_size.div_ceil(desc_size) * desc_size;
 
     // If our static buffer is too small, fall back to pool (rare)
     if buf_size > unsafe { MAP_WORK_BUF.len() } {
diff --git a/src/ps2.rs b/rsnix/src/ps2.rs
index 4ea8b7a..b83a4e0 100644
--- a/src/ps2.rs
+++ b/rsnix/src/ps2.rs
@@ -346,11 +346,10 @@ fn update_modifiers(scancode: u8, pressed: bool, e0: bool) {
         (0x1D, true) => set_mod(state, MOD_RCTRL, pressed),
         (0x38, false) => set_mod(state, MOD_LALT, pressed),
         (0x38, true) => set_mod(state, MOD_RALT, pressed),
-        (0x3A, false) => {
-            if pressed {
+        (0x3A, false)
+            if pressed => {
                 state.modifiers ^= MOD_CAPS;
             }
-        }
         _ => {}
     }
 }
diff --git a/src/serial.rs b/rsnix/src/serial.rs
index 03fa570..03fa570 100644
--- a/src/serial.rs
+++ b/rsnix/src/serial.rs
diff --git a/src/uefi.rs b/rsnix/src/uefi.rs
index 2e3ed6b..2e3ed6b 100644
--- a/src/uefi.rs
+++ b/rsnix/src/uefi.rs