feat(release): recursion guard for the health gate; run-task drift warning; M20 packages/* decision recorded (#39)

- release.sh health gate runs with MOSAIC_ENSURE_SKIP=1: the gated task run
  cannot re-enter release self-determination
- run-task.sh warns on release drift instead of silently using a stale image
- ROADMAP: M20 decision recorded (packages/* monorepo at usurpation,
  continuity-first); restructure sequenced as M20 phase 1

Closes #39

scripts/release.sh

@@ -49,7 +49,9 @@ health_check() { # returns 0 only when the marker path passes; $1 = fault inject
         task="$tmp/fault-task.json"
     fi
     local rc=0
-    scripts/run-task.sh run "$task" >/dev/null 2>&1 || rc=$?
+    # MOSAIC_ENSURE_SKIP: the gate's run must not re-enter release
+    # self-determination (recursion guard).
+    MOSAIC_ENSURE_SKIP=1 scripts/run-task.sh run "$task" >/dev/null 2>&1 || rc=$?
     [ -n "$tmp" ] && rm -rf "$tmp"
     return "$rc"
 }