Clean up warnings, fix FAT32 multi-cluster dirs, prep for edition 2024

Warning cleanup (cargo check + clippy now 0 across the workspace):
- Migrate all 21 static_mut_refs sites to &raw mut accessors (fat, gop,
  ps2, vt, ahci, interrupts, memory) so edition 2024 won't deny them
- panic = "abort" profiles: bare cargo check/build now works without
  nightly/-Zbuild-std
- Wire TICKS in the timer ISR (it was never incremented, so the vt scroll
  batching trigger was dead code)
- Clippy: efi_main becomes unsafe extern "efiapi" with a # Safety doc,
  KeyBuf::new uses inline-const array repeat (no interior-mutable const),
  editor main loop is a while-let, PIT control byte regrouped
- [workspace.lints.clippy] allows result_unit_err + needless_range_loop
  (deliberate kernel style); large_enum_variant allowed on LineInput
- Drop now-stale static_mut_refs allow from the rsdos bin

FAT32 correctness fixes (both pre-existing, exposed by the SFN fix):
- Unique 8.3 short names: to_8_3() never disambiguated collisions, so
  files sharing a long-name prefix got identical SFNs and fsck reported
  duplicate directory entries.  Add dir_short_names() + unique_short_name()
  (~N tails, Windows-style) and force LFN when the SFN changes.
- Multi-cluster directories: scan_dir/dir_short_names stopped at the first
  0x00 slot, hiding every entry written into a chained cluster (writes
  failed with 'cannot write', duplicate SFNs accumulated); add_dir_entry
  now packs the cluster (0xE5 deleted-markers) before extending so other
  FAT readers (mtools, Windows) see the continuation too.

Other: delete dead fields (Disk.fis, Volume.fat_count), drop timer_irq/
keyboard_irq/rendered, refresh_and_exit is a documented unsafe fn, CONTEXT
.md corrected (stable toolchain, IRQ input, 4-crate layout), .gitignore
excludes .pi-subagents artifacts.

Validated: cargo check/clippy/fmt clean, make test-disk PASS on fresh and
reused images (incl. two directory-chain extensions and ~10 SFN tails),
editor round-trip smoke test PASS.

2 files changed, 15 insertions, 14 deletions

diff --git a/rsdos/Cargo.toml b/rsdos/Cargo.toml
index 5bf83fe..d09bd70 100644
--- a/rsdos/Cargo.toml
+++ b/rsdos/Cargo.toml
@@ -3,6 +3,9 @@ name = "rsdos"
 version.workspace = true
 edition.workspace = true
 
+[lints]
+workspace = true
+
 [dependencies]
 rsnix = { path = "../rsnix" }
 shell = { path = "../shell" }
diff --git a/rsdos/src/main.rs b/rsdos/src/main.rs
index e6b7d2a..2ba5d32 100644
--- a/rsdos/src/main.rs
+++ b/rsdos/src/main.rs
@@ -1,6 +1,6 @@
 #![no_std]
 #![no_main]
-#![allow(static_mut_refs, unsafe_code)]
+#![allow(unsafe_code)]
 
 use core::panic::PanicInfo;
 use rsnix::uefi::*;
@@ -31,8 +31,15 @@ fn panic(info: &PanicInfo) -> ! {
 // ---------------------------------------------------------------------------
 // EFI entry point
 // ---------------------------------------------------------------------------
+/// EFI entry point.
+///
+/// # Safety
+///
+/// The firmware hands us raw pointers (image handle, system table) that
+/// must remain valid for the lifetime of the call — a contract guaranteed
+/// by the UEFI loader.
 #[no_mangle]
-pub extern "efiapi" fn efi_main(image_handle: Handle, system_table: *mut SystemTable) -> ! {
+pub unsafe extern "efiapi" fn efi_main(image_handle: Handle, system_table: *mut SystemTable) -> ! {
     let st = unsafe { &mut *system_table };
     let bs = unsafe { &mut *st.boot_services };
     let con_out = unsafe { &mut *st.con_out };
@@ -83,22 +90,13 @@ pub extern "efiapi" fn efi_main(image_handle: Handle, system_table: *mut SystemT
         rsnix::serial_println!("gop: not found (0x{:x})", gop_result);
     }
     rsnix::vt::init();
-    rsnix::serial_println!(
-        "vt: terminal ready ({}x{})",
-        {
-            let (rows, cols) = rsnix::vt::size();
-            rows
-        },
-        {
-            let (rows, cols) = rsnix::vt::size();
-            cols
-        }
-    );
+    let (rows, cols) = rsnix::vt::size();
+    rsnix::serial_println!("vt: terminal ready ({}x{})", rows, cols);
 
     // ExitBootServices — we now own the machine
     if unsafe { (bs.exit_boot_services)(image_handle, map_key) } != EFI_SUCCESS {
         rsnix::serial_println!("WARN: ExitBootServices failed, retrying...");
-        match rsnix::memory::refresh_and_exit(bs, image_handle) {
+        match unsafe { rsnix::memory::refresh_and_exit(bs, image_handle) } {
             Ok(_) => {}
             Err(e) => {
                 rsnix::serial_println!("FATAL: cannot ExitBootServices (0x{:x})", e);