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, 14 insertions, 12 deletions

diff --git a/rsnix/src/gop.rs b/rsnix/src/gop.rs
index 77cc514..0d24d7d 100644
--- a/rsnix/src/gop.rs
+++ b/rsnix/src/gop.rs
@@ -105,23 +105,25 @@ pub fn clear_screen() {
     crate::vt::clear_all();
 }
 
+/// Raw-pointer accessor for the framebuffer static (single-threaded
+/// kernel; keeps `static_mut_refs` quiet).
+fn fb() -> &'static mut Option<Framebuffer> {
+    unsafe { &mut *core::ptr::addr_of_mut!(FB) }
+}
+
 /// (cols, rows) of the text surface, from the current framebuffer mode.
 pub fn dims() -> (usize, usize) {
-    unsafe {
-        match FB.as_ref() {
-            Some(f) => (f.width / 8, f.height / 16),
-            None => (0, 0),
-        }
+    match fb().as_ref() {
+        Some(f) => (f.width / 8, f.height / 16),
+        None => (0, 0),
     }
 }
 
 /// Pack an (r, g, b) colour for the framebuffer's pixel format.
 pub fn rgb(r: u8, g: u8, b: u8) -> u32 {
-    unsafe {
-        match FB.as_ref() {
-            Some(f) if f.bgr => ((r as u32) << 16) | ((g as u32) << 8) | b as u32,
-            _ => ((b as u32) << 16) | ((g as u32) << 8) | r as u32,
-        }
+    match fb().as_ref() {
+        Some(f) if f.bgr => ((r as u32) << 16) | ((g as u32) << 8) | b as u32,
+        _ => ((b as u32) << 16) | ((g as u32) << 8) | r as u32,
     }
 }
 
@@ -340,7 +342,7 @@ fn unicode_glyph_bits(ch: u16) -> Option<[u8; 16]> {
 }
 
 pub(crate) fn blit_glyph(col: usize, row: usize, ch: u16, fg: (u8, u8, u8), bg: (u8, u8, u8)) {
-    if let Some(fb) = unsafe { FB.as_ref() } {
+    if let Some(fb) = fb().as_ref() {
         let glyph = font::GLYPH_8X16;
         let data = if ch < 256 {
             match glyph.get(ch as usize) {
@@ -381,7 +383,7 @@ pub(crate) fn blit_glyph(col: usize, row: usize, ch: u16, fg: (u8, u8, u8), bg:
 /// Shift the framebuffer content up `n` text rows and clear the exposed
 /// bottom rows.  `n` batches deferred scrolls into one push.
 pub(crate) fn shift_up_n(n: usize) {
-    if let Some(fb) = unsafe { FB.as_ref() } {
+    if let Some(fb) = fb().as_ref() {
         fb.shift_up_n(n);
     }
 }