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/python-on-danos.md

@@ -257,5 +257,5 @@ in practice cares.
   the spawn-argv work extends.
 - [device-driver-development/ipc.md](device-driver-development/ipc.md) — the IPC
   surface Python services speak.
-- [file-system-development/danos-file-system-hierarchy-FSH.md](file-system-development/danos-file-system-hierarchy-FSH.md)
+- [file-system-development/file-system-hierarchy.md](file-system-development/file-system-hierarchy.md)
   — where `Lib/` and `site-packages` land on the image.