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.

1 files changed, 5 insertions, 3 deletions

diff --git a/rsnix/src/ahci.rs b/rsnix/src/ahci.rs
index 427345d..9a49431 100644
--- a/rsnix/src/ahci.rs
+++ b/rsnix/src/ahci.rs
@@ -54,7 +54,6 @@ const ATA_WRITE_DMA_EXT: u8 = 0x35;
 struct Disk {
     port: usize,  // port register base = ABAR + 0x100
     clb: usize,   // command list, 1024 B (32 × 32 B), 256 B aligned
-    fis: usize,   // FIS receive area, 256 B aligned
     ct: usize,    // command table, 256 B, 128 B aligned
     buf: usize,   // 4 KiB DMA data buffer (page aligned)
     sectors: u64, // total sectors (LBA48 from IDENTIFY)
@@ -175,7 +174,6 @@ fn start_port(abar: usize, port_idx: u32) -> Option<Disk> {
     let mut d = Disk {
         port,
         clb,
-        fis,
         ct,
         buf,
         sectors: 0,
@@ -389,8 +387,12 @@ fn issue(d: &Disk, cmd: u8, lba: u64, count: u32, write: bool) -> Result<(), ()>
     Ok(())
 }
 
+fn disks() -> &'static mut [Option<Disk>; MAX_DISKS] {
+    unsafe { &mut *core::ptr::addr_of_mut!(DISKS) }
+}
+
 fn active() -> Option<&'static Disk> {
-    unsafe { DISKS.get(ACTIVE).and_then(|d| d.as_ref()) }
+    disks().get(unsafe { ACTIVE }).and_then(|d| d.as_ref())
 }
 
 /// DMA `count` sectors starting at `lba` into the selected disk's buffer.