engram: WAL persistence + integrity hardening + single canonical runtime

Establish lang/runtime/ as the ONE canonical el runtime (from the active
runtime that carries hebb/emb persistence + the new WAL); repoint the el CI
publish, engram build, elb default, and in-repo build scripts to it; delete
the el-compiler/runtime + lang/releases/ forks; add scripts/check-single-runtime.sh
drift guard.

Fixes a live prod bug: the el CI published el-runtime-c/-h from the LAGGING
el-compiler fork (0 hebb refs), so the shipped soul never persisted Hebbian
edge weights — learned co-activation was wiped on every restart. Publishing
from canonical ships the stranded 'learning that cannot outlive the process'
fix.

WAL storage engine + integrity fixes (DELETE->tombstone + store-layer
protection, safe data-dir default) ride in behind ENGRAM_WAL (default off =
byte-identical to today). Verified: engram elb per-module build clean, WAL
gate 66/66, native smoke ok, drift-guard green.

lang/runtime/json.el

@@ -2,7 +2,7 @@
 //
 // Thin El wrappers over seed JSON primitives, plus pure-El builders and
 // helpers.  Each function here corresponds to (and replaces) a C function
-// from el-compiler/runtime/legacy/el_runtime.c (lines 2692–3333).
+// from runtime/el_runtime.c (lines 2692–3333).
 //
 // Seed primitives consumed by this module:
 //   __json_get(json, key)              -> String   (value as string)