docs: the communication stack — /protocol namespace, layered model, non-unix hierarchy, SMEP/SMAP plan

The security-track design set. communication.md is the model: four layers
(namespace / protocol / channel / transport), packets and signals, parties
addressed by the channel and objects by target, transports as replaceable
buffer+doorbell mechanisms. protocol-namespace.md is L3+L2: /protocol names
contracts, resolution establishes a channel, init is the registrar,
restriction is per-process namespace delegation (with the microphone-prompt
worked example), the envelope is the universal packet header, migration
P1-P5 retires ServiceId. file-system-hierarchy.md replaces the unix-FHS
spec with the danos-native tree (/applications, /protocol, /system,
/volumes) and its migration table. ipc.md is re-cut as the kernel-ipc
transport document. smep-smap.md designs the kernel hardening: copy
discipline for the eight raw user-pointer syscalls, then SMEP, then SMAP
as a permanent tripwire.

docs/zig-self-hosting.md

@@ -347,7 +347,7 @@ Two current decisions fall out of this roadmap:
 - [syscall.md](os-development/syscall.md) — the kernel↔runtime ABI `runtime.os` is built on.
 - [sysv.md](os-development/sysv.md) — the entry stack (`argc/argv/envp/auxv`) danos already constructs.
 - [ipc.md](device-driver-development/ipc.md) — the IPC the VFS/FAT operations travel over.
-- [danos-file-system-hierarchy-FSH.md](file-system-development/danos-file-system-hierarchy-FSH.md) — the
+- [file-system-hierarchy.md](file-system-development/file-system-hierarchy.md) — the
   filesystem layout the file surface serves.
 - [coding-standards.md](coding-standards.md) — danos naming (why the compat spellings
   are confined, and now retired).