Comprehensive cleanup: docs, edition 2024, new examples, build fixes (#3)

* Refactor: fix bugs, harden safety, and reduce duplication

- Fix off-by-one bounds check in embedded_graphics (0..=480 -> 0..480)
- Replace static mut VRAM_BASE with AtomicPtr in debug.rs
- Extract shared open_psp_file() helper in test_runner.rs
- DRY fminf/fmaxf into nan_aware_vfpu_op! macro in math/mod.rs
- Modernize mksfo.rs: if-let over contains_key+unwrap, iterator chains,
  bounds checking on fixed-size buffer writes
- Replace magic numbers with named constants in prxgen.rs (PF_R|PF_X,
  PRX_SEGMENT_ALIGN), replace unwrap() with .context()
- Simplify always-true u8 <= 255 check, add debug_assert for font index

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Refactor round 2: harden safety, improve clarity, reduce duplication

- Prevent double-panic by using Location::caller() fallback in panic handler
- Extract read_pixel<T> helper in screenshot.rs to DRY pixel format match arms
- Document allocator memory layout with ASCII diagram in alloc_impl.rs
- Unify prxmin.rs main to return Result<()> like other cargo-psp binaries
- Replace recursive tab expansion with loop in debug.rs
- Add Display impls for VramAllocatorInUseError and VramAllocError
- Consolidate redundant unsafe blocks in init_cwd (lib.rs)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Refactor round 3: fix critical gu.rs bugs, eliminate UB, harden allocators

Fix sceGuDisplay returning input instead of previous state, sceGuCheckList
using wrong pointer arithmetic, sceGuSetAllStatus transmuting arbitrary u32
to enum, callback_sig/callback_fin dropping the second argument, and
StencilOperation doc comment swaps. Replace all core::intrinsics::unreachable()
with safe unreachable!() macro across gu.rs, gum.rs, and vfpu_context.rs.
Guard both allocators against align_offset returning usize::MAX and add
checked_add overflow protection to std_support allocator. Fix mksfo defaults
overwriting user values, prxmin double-dot extension, debug.rs LineIter
off-by-one, embedded_graphics vram_base type mismatch, vram_alloc overflow,
benchmark division by zero, and screenshot unstable intrinsics. Extract
CONTEXTS array DRY, update paint-mode to edition 2024, remove stabilized
feature gates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Revise docs, upgrade examples to edition 2024, add file-io/screenshot/audio-tone examples

- Rewrite README.md: add API Overview table, Features section, Examples table; move changelog lower
- Fix AGENTS.md: replace stale kernel mode description with current capabilities
- Add KERNEL_MODE_PLAN.md completed status header
- Upgrade 15 examples from edition 2018/2021 to 2024
- Fix edition 2024 static_mut_refs: use &raw mut for all static mut access
- Fix VRAM allocator calls: add .unwrap() for Result returns
- Add 3 new examples: file-io (sceIo*), screenshot (screenshot_bmp), audio-tone (sceAudio*)
- Remove obsolete FromIterator import from ratatui example

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* Fix 3 pre-existing example build failures

- cube: regenerate ferris.bin at correct 128x128 RGBA size (was 65531 bytes, needs 65536)
- embedded-graphics: upgrade tinybmp 0.3.1 to 0.7.0 (fixes trait mismatch with embedded-graphics 0.8.1)
- rust-std-hello-world: auto-detect psp "std" feature in cargo-psp so RUST_PSP_BUILD_STD env var is no longer required

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: AI Agent Bot <ai-agent@localhost>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: 3 people

AGENTS.md

@@ -106,7 +106,7 @@ The `psp_extern!` macro generates syscall stubs with NIDs (numeric IDs) that the
 
 ### Kernel Mode (`--features kernel`)
 
-Enables privileged PSP APIs: kernel memory partitions, interrupt handlers, PRX module loading, volatile memory access. Uses `module_kernel!()` macro. Commented-out modules (`codec.rs`, `nand.rs`, `sircs.rs`) are planned for activation in kernel mode. See `KERNEL_MODE_PLAN.md` for the 6-phase implementation roadmap.
+Enables privileged PSP APIs: kernel memory partitions, interrupt handlers, PRX module loading, volatile memory access, NAND flash, IR remote (SIRCS), hardware codecs, ME coprocessor control, hardware register I/O, and exception handling. Uses `module_kernel!()` macro. Key modules: `me.rs` (Media Engine boot/task), `hw.rs` (register I/O), `sys/nand.rs`, `sys/sircs.rs`, `sys/codec.rs`.
 
 ## Key Conventions
 

Cargo.lock

@@ -1,5 +1,9 @@
 # Kernel Mode Implementation Plan
 
+> **Status: COMPLETED** -- All 6 phases were implemented in commit `6f01ff8`. This document is retained as historical record of the design process.
+
+---
+
 This plan covers all work needed to bring the rust-psp SDK to full kernel mode support. The primary consumer is [OASIS_OS](https://github.com/AndrewAltimit/template-repo/tree/main/packages/oasis_os), but all changes are general-purpose SDK extensions useful to any PSP homebrew project.
 
 **Branch:** `initial_release`