docs(v4): MESH step 7 done -- a second unit, PAUSE, RESUME, KILL; acceptance

MESH.md step 7: what was built, the tests, the (DOWN) mend, the traced
(LOST) finding; 9a.5: a centre killed mid-birth, and birth authority not
yet tied to identity.  v4/README.md: births follow v3.

Acceptance at this commit's code: amd64, aarch64, riscv64 clean qemu, v4:
ok>, POST 538/538, dict_hash=0x248b4edc47f4357e on all three; test-32 0
failures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

v4/README.md

@@ -134,6 +134,11 @@ time, and joins four such nodes in a square round her
 The two products are not yet this: they become the five nodes at steps 8
 and 9.
 A node she births is not POSTed: POST is the kernel's, once, on Hera.
+Since 2026-10-16 births follow v3 (`MESH.md` 9, 9a, step 7): any node may
+birth on its own ports and is its children's parent; Hera alone kills,
+pauses and resumes, by number, through the kernel's registry
+(`capsules/v4/centre.4th`, `hera.4th`); a second unit is born by its own
+centre, and a GONE goes down the birth graph.
 
 **Refusals and waits** (`MESH.md` 7b, step 6c). A wait on a node that
 never answers -- stuck, or gone -- is ended by Hera's killing it, which