Judge tests that read another repository against what the check clones, never the desktop's checkout (issue 432)

Tests that read ../../../mesh-catalog or ../../../mesh-host gave a verdict
that depended on what sat beside the checkout: a stale or dirty sibling
failed them on a desktop, and a missing one skipped them unseen. They now
read the clone the build seat puts in MESH_CHECK_BESIDE, failing when it is
absent there, and elsewhere a copy captured at a named commit.

The skip had hidden that the builder test read a module retired by ADR 0190.
The systemd reading test no longer counts the machine's own environment.d.

testdata/beside/mesh-catalog/modules/slack/module.json.captured

@@ -0,0 +1,35 @@
+{
+  "module": "slack",
+  "version": "1",
+  "requires": [
+    "x11-display"
+  ],
+  "tools": [
+    "slack_status",
+    "slack_log",
+    "slack_restart",
+    "slack_check"
+  ],
+  "build": {
+    "artifacts": [
+      {
+        "name": "tools",
+        "kind": "bundle",
+        "language": "go",
+        "system": "arch",
+        "from": "cmd/slack-tools",
+        "binary": "slack-tools",
+        "loads": [
+          "slack-tools"
+        ]
+      }
+    ]
+  },
+  "contributions": [
+    {
+      "seat": "node-display-session",
+      "kind": "config",
+      "content": "# Slack (module slack, novox/hq ADR 0208, ADR 0212). Owned by the mesh: replaced at every push.\n# Its one start: at login, to the tray (-s), with the arguments of the package's own desktop entry.\n# No XDG autostart entry starts it as well; slack_check names one if it appears.\nexec --no-startup-id /usr/bin/slack --gtk-version=3 -s\n# The chat window. Slack owns four X windows, and the only one i3 manages has the class \"slack\" in\n# lower case; the three of class \"Slack\" (the packaged entry's StartupWMClass) are its unmanaged\n# helpers and its tray icon, so a rule on class=\"Slack\" matches nothing. window_role keeps a call or\n# screen-share window out of the rules. $ws3 is i3's, in scope here.\nfor_window [class=\"(?i)^slack$\" window_role=\"browser-window\"] move to workspace $ws3\nfor_window [class=\"(?i)^slack$\" window_role=\"browser-window\"] floating disable\nfor_window [class=\"(?i)^slack$\" window_role=\"browser-window\"] border pixel 2\n"
+    }
+  ]
+}