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>

internal/monitoring/alertmanager_test.go

@@ -0,0 +1,175 @@
+package monitoring
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestAlertmanagerClient_ListAlerts(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v2/alerts" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[
+			{
+				"annotations": {"summary": "Target is down"},
+				"endsAt": "2024-01-01T01:00:00Z",
+				"fingerprint": "abc123",
+				"receivers": [{"name": "default"}],
+				"startsAt": "2024-01-01T00:00:00Z",
+				"status": {"inhibitedBy": [], "silencedBy": [], "state": "active"},
+				"updatedAt": "2024-01-01T00:00:00Z",
+				"generatorURL": "http://prometheus:9090/graph",
+				"labels": {"alertname": "TargetDown", "severity": "critical", "instance": "node1:9100"}
+			}
+		]`))
+	}))
+	defer srv.Close()
+
+	client := NewAlertmanagerClient(srv.URL)
+	alerts, err := client.ListAlerts(context.Background(), AlertFilters{})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(alerts) != 1 {
+		t.Fatalf("expected 1 alert, got %d", len(alerts))
+	}
+	if alerts[0].Fingerprint != "abc123" {
+		t.Errorf("expected fingerprint=abc123, got %s", alerts[0].Fingerprint)
+	}
+	if alerts[0].Labels["alertname"] != "TargetDown" {
+		t.Errorf("expected alertname=TargetDown, got %s", alerts[0].Labels["alertname"])
+	}
+	if alerts[0].Status.State != "active" {
+		t.Errorf("expected state=active, got %s", alerts[0].Status.State)
+	}
+}
+
+func TestAlertmanagerClient_ListAlertsWithFilters(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		q := r.URL.Query()
+		if q.Get("active") != "true" {
+			t.Errorf("expected active=true, got %s", q.Get("active"))
+		}
+		if q.Get("silenced") != "false" {
+			t.Errorf("expected silenced=false, got %s", q.Get("silenced"))
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[]`))
+	}))
+	defer srv.Close()
+
+	client := NewAlertmanagerClient(srv.URL)
+	active := true
+	silenced := false
+	_, err := client.ListAlerts(context.Background(), AlertFilters{
+		Active:   &active,
+		Silenced: &silenced,
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+}
+
+func TestAlertmanagerClient_ListSilences(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/v2/silences" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[
+			{
+				"id": "silence-1",
+				"matchers": [{"name": "alertname", "value": "TargetDown", "isRegex": false}],
+				"startsAt": "2024-01-01T00:00:00Z",
+				"endsAt": "2024-01-01T02:00:00Z",
+				"createdBy": "admin",
+				"comment": "Maintenance window",
+				"status": {"state": "active"}
+			}
+		]`))
+	}))
+	defer srv.Close()
+
+	client := NewAlertmanagerClient(srv.URL)
+	silences, err := client.ListSilences(context.Background())
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if len(silences) != 1 {
+		t.Fatalf("expected 1 silence, got %d", len(silences))
+	}
+	if silences[0].ID != "silence-1" {
+		t.Errorf("expected id=silence-1, got %s", silences[0].ID)
+	}
+	if silences[0].CreatedBy != "admin" {
+		t.Errorf("expected createdBy=admin, got %s", silences[0].CreatedBy)
+	}
+}
+
+func TestAlertmanagerClient_CreateSilence(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if r.URL.Path != "/api/v2/silences" {
+			t.Errorf("unexpected path: %s", r.URL.Path)
+		}
+		if r.Header.Get("Content-Type") != "application/json" {
+			t.Errorf("expected Content-Type=application/json, got %s", r.Header.Get("Content-Type"))
+		}
+
+		var silence Silence
+		if err := json.NewDecoder(r.Body).Decode(&silence); err != nil {
+			t.Fatalf("failed to decode request body: %v", err)
+		}
+		if silence.CreatedBy != "admin" {
+			t.Errorf("expected createdBy=admin, got %s", silence.CreatedBy)
+		}
+
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{"silenceID": "new-silence-id"}`))
+	}))
+	defer srv.Close()
+
+	client := NewAlertmanagerClient(srv.URL)
+	id, err := client.CreateSilence(context.Background(), Silence{
+		Matchers: []Matcher{
+			{Name: "alertname", Value: "TargetDown", IsRegex: false},
+		},
+		StartsAt:  time.Now(),
+		EndsAt:    time.Now().Add(2 * time.Hour),
+		CreatedBy: "admin",
+		Comment:   "Test silence",
+	})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if id != "new-silence-id" {
+		t.Errorf("expected id=new-silence-id, got %s", id)
+	}
+}
+
+func TestAlertmanagerClient_HTTPError(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = w.Write([]byte("internal error"))
+	}))
+	defer srv.Close()
+
+	client := NewAlertmanagerClient(srv.URL)
+	_, err := client.ListAlerts(context.Background(), AlertFilters{})
+	if err == nil {
+		t.Fatal("expected error, got nil")
+	}
+}