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/prometheus.go

@@ -0,0 +1,135 @@
+package monitoring
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// PrometheusClient is an HTTP client for the Prometheus API.
+type PrometheusClient struct {
+	baseURL    string
+	httpClient *http.Client
+}
+
+// NewPrometheusClient creates a new Prometheus API client.
+func NewPrometheusClient(baseURL string) *PrometheusClient {
+	return &PrometheusClient{
+		baseURL: strings.TrimRight(baseURL, "/"),
+		httpClient: &http.Client{
+			Timeout: 30 * time.Second,
+		},
+	}
+}
+
+// Query executes an instant PromQL query. If ts is zero, the current time is used.
+func (c *PrometheusClient) Query(ctx context.Context, promql string, ts time.Time) (*PromQueryData, error) {
+	params := url.Values{}
+	params.Set("query", promql)
+	if !ts.IsZero() {
+		params.Set("time", fmt.Sprintf("%d", ts.Unix()))
+	}
+
+	body, err := c.get(ctx, "/api/v1/query", params)
+	if err != nil {
+		return nil, fmt.Errorf("query failed: %w", err)
+	}
+
+	var data PromQueryData
+	if err := json.Unmarshal(body, &data); err != nil {
+		return nil, fmt.Errorf("failed to parse query data: %w", err)
+	}
+	return &data, nil
+}
+
+// LabelValues returns all values for a given label name.
+func (c *PrometheusClient) LabelValues(ctx context.Context, label string) ([]string, error) {
+	path := fmt.Sprintf("/api/v1/label/%s/values", url.PathEscape(label))
+	body, err := c.get(ctx, path, nil)
+	if err != nil {
+		return nil, fmt.Errorf("label values failed: %w", err)
+	}
+
+	var values []string
+	if err := json.Unmarshal(body, &values); err != nil {
+		return nil, fmt.Errorf("failed to parse label values: %w", err)
+	}
+	return values, nil
+}
+
+// Metadata returns metadata for metrics. If metric is empty, returns metadata for all metrics.
+func (c *PrometheusClient) Metadata(ctx context.Context, metric string) (map[string][]PromMetadata, error) {
+	params := url.Values{}
+	if metric != "" {
+		params.Set("metric", metric)
+	}
+
+	body, err := c.get(ctx, "/api/v1/metadata", params)
+	if err != nil {
+		return nil, fmt.Errorf("metadata failed: %w", err)
+	}
+
+	var metadata map[string][]PromMetadata
+	if err := json.Unmarshal(body, &metadata); err != nil {
+		return nil, fmt.Errorf("failed to parse metadata: %w", err)
+	}
+	return metadata, nil
+}
+
+// Targets returns the current scrape targets.
+func (c *PrometheusClient) Targets(ctx context.Context) (*PromTargetsData, error) {
+	body, err := c.get(ctx, "/api/v1/targets", nil)
+	if err != nil {
+		return nil, fmt.Errorf("targets failed: %w", err)
+	}
+
+	var data PromTargetsData
+	if err := json.Unmarshal(body, &data); err != nil {
+		return nil, fmt.Errorf("failed to parse targets data: %w", err)
+	}
+	return &data, nil
+}
+
+// get performs a GET request and returns the "data" field from the Prometheus response envelope.
+func (c *PrometheusClient) get(ctx context.Context, path string, params url.Values) (json.RawMessage, error) {
+	u := c.baseURL + path
+	if len(params) > 0 {
+		u += "?" + params.Encode()
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, u, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create request: %w", err)
+	}
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("request failed: %w", err)
+	}
+	defer resp.Body.Close() //nolint:errcheck // cleanup on exit
+
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read response: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("unexpected status %d: %s", resp.StatusCode, string(body))
+	}
+
+	var promResp PromResponse
+	if err := json.Unmarshal(body, &promResp); err != nil {
+		return nil, fmt.Errorf("failed to parse response: %w", err)
+	}
+
+	if promResp.Status != "success" {
+		return nil, fmt.Errorf("prometheus error (%s): %s", promResp.ErrorType, promResp.Error)
+	}
+
+	return promResp.Data, nil
+}