feat: harness VM stack (runner, measure-db, blackbox, Alloy, k6) and the 12 scenarios

Experiment design 5 and 7 for the harness VM (10.20.0.11): vm/harness/apply.sh pulls the secrets from Secret Manager,
compose runs runner:de076a7, measure-db, blackbox, Alloy (probe_success -> Mimir) and k6 under the campaign profile.
Scenario files C-K1..X-M2 are loaded by the runner. Harness ClusterRole gains replicasets get/list for rollout undo.

vm/harness/scenarios/V-G2.yaml

@@ -0,0 +1,18 @@
+# design 7 V-G2: grey zone, VM. Pause WAL replay on db-replica; no SLO impact, only DbReplicationLag fires. Correct: db.replay_resume after approval.
+id: V-G2
+path: gray
+asset: vm
+expected_layer: 2
+ground_truth_label: replication_paused
+ground_truth_action: db.replay_resume
+description: SELECT pg_wal_replay_pause() on db-replica (harness role)
+inject:
+  method: psql
+  host: db-replica
+  database: postgres
+  sql: SELECT pg_wal_replay_pause()
+revert:
+  method: psql
+  host: db-replica
+  database: postgres
+  sql: SELECT pg_wal_replay_resume()