docs: comprehensive documentation update reflecting current AdrOS state

docs: comprehensive documentation update reflecting current AdrOS state

Updated all 4 documentation files to accurately reflect the current codebase:

POSIX_ROADMAP.md:
- fork now marked as CoW (was 'full copy')
- execve marked complete (was partial)
- brk/sbrk, nanosleep, clock_gettime marked implemented
- O_CLOEXEC, FD_CLOEXEC marked implemented
- Signal defaults marked complete (Ctrl+C/Z/D/\)
- Raw TTY mode, TIOCGWINSZ marked implemented
- PMM now shows spinlock + refcount
- Slab allocator, CoW, shared memory, SMEP marked implemented
- Heap shows dynamic growth to 64MB
- PCI, ATA DMA, LAPIC/IOAPIC, SMP, ACPI, VBE, SYSENTER, CPUID added
- ulibc marked implemented
- procfs partial noted
- Priority roadmap updated: 9 items marked done, remaining reordered

SUPPLEMENTARY_ANALYSIS.md:
- POSIX score updated from ~45% to ~70%
- PMM: spinlock + refcount now implemented
- VMM: CoW + SMEP now implemented
- Heap: slab allocator + dynamic growth now implemented
- Scheduler: O(1) with bitmap now implemented
- TTY: raw mode, signal chars, TIOCGWINSZ now implemented
- Userland: ulibc + SYSENTER now implemented
- Drivers: PCI, ATA DMA, LAPIC/IOAPIC, SMP, ACPI, VBE now implemented
- Advanced: CoW, slab, shmem now implemented
- Part 3 comparison table updated (AdrOS ahead in 5/10 dimensions)
- Part 4 recommendations: 9 items marked completed, remaining reordered

README.md:
- Complete rewrite of Features section with organized subsections
- Added: Memory Management, Process & Scheduling, Syscalls, TTY/PTY,
  Filesystems (6 types), Drivers & Hardware, Userland, Security, Testing
- Updated TODO with near-term/medium-term/long-term priorities
- Updated Directory Structure with new paths

BUILD_GUIDE.md:
- Added expect and sparse to dependencies
- Added Testing section with all make targets
- Increased smoke test timeout from 40s to 60s