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.go

@@ -0,0 +1,153 @@
+package monitoring
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// AlertmanagerClient is an HTTP client for the Alertmanager API v2.
+type AlertmanagerClient struct {
+	baseURL    string
+	httpClient *http.Client
+}
+
+// NewAlertmanagerClient creates a new Alertmanager API client.
+func NewAlertmanagerClient(baseURL string) *AlertmanagerClient {
+	return &AlertmanagerClient{
+		baseURL: strings.TrimRight(baseURL, "/"),
+		httpClient: &http.Client{
+			Timeout: 30 * time.Second,
+		},
+	}
+}
+
+// ListAlerts returns alerts matching the given filters.
+func (c *AlertmanagerClient) ListAlerts(ctx context.Context, filters AlertFilters) ([]Alert, error) {
+	params := url.Values{}
+
+	if filters.Active != nil {
+		params.Set("active", fmt.Sprintf("%t", *filters.Active))
+	}
+	if filters.Silenced != nil {
+		params.Set("silenced", fmt.Sprintf("%t", *filters.Silenced))
+	}
+	if filters.Inhibited != nil {
+		params.Set("inhibited", fmt.Sprintf("%t", *filters.Inhibited))
+	}
+	if filters.Unprocessed != nil {
+		params.Set("unprocessed", fmt.Sprintf("%t", *filters.Unprocessed))
+	}
+	if filters.Receiver != "" {
+		params.Set("receiver", filters.Receiver)
+	}
+	for _, f := range filters.Filter {
+		params.Add("filter", f)
+	}
+
+	u := c.baseURL + "/api/v2/alerts"
+	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 alerts []Alert
+	if err := json.Unmarshal(body, &alerts); err != nil {
+		return nil, fmt.Errorf("failed to parse alerts: %w", err)
+	}
+
+	return alerts, nil
+}
+
+// ListSilences returns all silences.
+func (c *AlertmanagerClient) ListSilences(ctx context.Context) ([]Silence, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, c.baseURL+"/api/v2/silences", 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 silences []Silence
+	if err := json.Unmarshal(body, &silences); err != nil {
+		return nil, fmt.Errorf("failed to parse silences: %w", err)
+	}
+
+	return silences, nil
+}
+
+// CreateSilence creates a new silence and returns the silence ID.
+func (c *AlertmanagerClient) CreateSilence(ctx context.Context, silence Silence) (string, error) {
+	data, err := json.Marshal(silence)
+	if err != nil {
+		return "", fmt.Errorf("failed to marshal silence: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, c.baseURL+"/api/v2/silences", bytes.NewReader(data))
+	if err != nil {
+		return "", fmt.Errorf("failed to create request: %w", err)
+	}
+	req.Header.Set("Content-Type", "application/json")
+
+	resp, err := c.httpClient.Do(req)
+	if err != nil {
+		return "", 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 "", fmt.Errorf("failed to read response: %w", err)
+	}
+
+	if resp.StatusCode != http.StatusOK {
+		return "", fmt.Errorf("unexpected status %d: %s", resp.StatusCode, string(body))
+	}
+
+	var result struct {
+		SilenceID string `json:"silenceID"`
+	}
+	if err := json.Unmarshal(body, &result); err != nil {
+		return "", fmt.Errorf("failed to parse response: %w", err)
+	}
+
+	return result.SilenceID, nil
+}