Phase 4 - IPC Topic Refactor

Phase 4 reorganizes the Day53-Day58 IPC materials into topic-based documentation and API references.

Added Topic Pages

• UNIX Domain Socket
• File Descriptor Passing
• POSIX Shared Memory
• POSIX Message Queue
• POSIX Semaphore

Added API Reference Pages

• socketpair
• sendmsg / recvmsg
• SCM_RIGHTS
• shm_open
• mmap
• mq_open
• sem_init
• Process-shared pthread synchronization

Design Goal

The IPC section now provides a review path from local socket IPC to shared memory and synchronization.

UNIX Domain Socket
        ↓
File Descriptor Passing
        ↓
POSIX Shared Memory
        ↓
POSIX Message Queue
        ↓
POSIX Semaphore

Validation

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