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>

cmd/nixpkgs-search/main.go

@@ -20,7 +20,7 @@ import (
 
 const (
 	defaultDatabase = "sqlite://nixpkgs-search.db"
-	version         = "0.2.0"
+	version         = "0.2.1"
 )
 
 func main() {