feat: consolidate DeadOS v2.0-v4.2 development

[assada]

Squashed development timeline:

2026-06-09

• v2.0: replace the original kernel with a Multiboot higher-half design.
• Add GDT, TSS, IDT, PIC, PIT, exception handling, and ring 3 entry.
• Add frame allocation, per-process paging, the kernel heap, and self-tests.
• Add the TTY, PS/2 keyboard, serial input, RTC, and VGA console.
• Add ELF processes, preemptive scheduling, VFS, syscalls, libc, and shell.
• v2.1: add pipes, redirection, writable ramfs, and Ctrl+C delivery.
• v2.2: add copy-on-write fork with frame reference counting.
• v2.3: add ATA PIO, FAT16 storage, and reboot persistence checks.
• v2.4: add FAT16 subdirectories, VFAT long names, mkdir, and rmdir.
• v2.5: add rename, lseek, zero-filled holes, and the block cache.

2026-06-10

• v2.6: add user signal handlers and the sigreturn trampoline.
• v2.7: add raw TTY mode, shell history, line editing, and ANSI color.
• v2.8: add per-process working directories, cd, pwd, and touch.
• v2.9: add xterm-style VGA scrollback.
• v3.0: expand libc and add the full-screen source editor.
• v3.1: port TCC and add per-process x87 state handling.
• v3.2: make TCC self-hosting with byte-identical bootstrap output.
• v3.3: add first-boot installation and the persistent disk toolchain.
• v3.4: add stat, file timestamps, home directories, and an improved ls.
• v3.5: add raw PS/2 scan-code input and game-oriented libc support.
• v3.6: add direct VGA mode 13h with automatic console restoration.
• v3.7: port PureDOOM and ship the shareware data set.

2026-07-09

• Complete the DOOM platform layer and in-system build path.
• v3.8: add guarded kernel stacks, canaries, entropy, and double-fault recovery.
• v3.9: add clone, futexes, thread groups, and the pthread foundation.
• Add the threaded runtime demo and scheduler stress coverage.
• v4.0: build non-bootstrap userland with the installed TCC toolchain.
• v4.1: complete pthread attributes, joins, TSD, atfork, and synchronization.

2026-07-10

• v4.2: add the display ABI, shared buffers, AF_UNIX IPC, PTYs, and input master.
• Add deadwm, deadterm, windowed DOOM, fullscreen mode, and VGA fallback.
• Add desktop lifecycle, recovery, performance, and regression coverage.
• Finalize the build defaults and public project documentation.