feat: add lab-monitoring MCP server for Prometheus and Alertmanager

New MCP server that queries live Prometheus and Alertmanager HTTP APIs
with 8 tools: list_alerts, get_alert, search_metrics, get_metric_metadata,
query (PromQL), list_targets, list_silences, and create_silence.

Extends the MCP core with ModeCustom and NewGenericServer for servers
that don't require a database. Includes CLI with direct commands
(alerts, query, targets, metrics), NixOS module, and comprehensive
httptest-based tests.

Bumps existing binaries to 0.2.1 due to shared internal/mcp change.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.mcp.json

@@ -25,6 +25,19 @@
       "env": {
         "NIXPKGS_SEARCH_DATABASE": "sqlite://:memory:"
       }
+    },
+    "lab-monitoring": {
+      "command": "nix",
+      "args": [
+        "run",
+        ".#lab-monitoring",
+        "--",
+        "serve"
+      ],
+      "env": {
+        "PROMETHEUS_URL": "http://localhost:9090",
+        "ALERTMANAGER_URL": "http://localhost:9093"
+      }
     }
   }
 }