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/tests/runtime/string_test.el

@@ -14,8 +14,8 @@
 //       tests/runtime/string_test.el > /tmp/string_test_combined.el
 //
 //   ./dist/platform/elc /tmp/string_test_combined.el > /tmp/string_test.c
-//   cc -std=c11 -I el-compiler/runtime -lcurl -lpthread \
-//      -o /tmp/string_test /tmp/string_test.c el-compiler/runtime/el_seed.c
+//   cc -std=c11 -I runtime -lcurl -lpthread \
+//      -o /tmp/string_test /tmp/string_test.c runtime/el_seed.c
 //   /tmp/string_test; echo "exit: $?"
 //
 // Exit code equals the number of failing assertions (0 = all pass).