Separate web UI into standalone metacrypt-web binary

The vault server holds in-memory unsealed state (KEK, engine keys) that
is lost on restart, requiring a full unseal ceremony. Previously the web
UI ran inside the vault process, so any UI change forced a restart and
re-unseal.

This change extracts the web UI into a separate metacrypt-web binary
that communicates with the vault over an authenticated gRPC connection.
The web server carries no sealed state and can be restarted freely.

- gen/metacrypt/v1/: generated Go bindings from proto/metacrypt/v1/
- internal/grpcserver/: full gRPC server implementation (System, Auth,
  Engine, PKI, Policy, ACME services) with seal/auth/admin interceptors
- internal/webserver/: web server with gRPC vault client; templates
  embedded via web/embed.go (no runtime web/ directory needed)
- cmd/metacrypt-web/: standalone binary entry point
- internal/config: added [web] section (listen_addr, vault_grpc, etc.)
- internal/server/routes.go: removed all web UI routes and handlers
- cmd/metacrypt/server.go: starts gRPC server alongside HTTP server
- Deploy: Dockerfile builds both binaries, docker-compose adds
  metacrypt-web service, new metacrypt-web.service systemd unit,
  Makefile gains proto/metacrypt-web targets

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/metacrypt-web/main.go

@@ -0,0 +1,75 @@
+// metacrypt-web is the standalone web UI server for Metacrypt.
+// It communicates with the vault over gRPC and can be restarted independently
+// without requiring the vault to be re-unsealed.
+package main
+
+import (
+	"context"
+	"fmt"
+	"log/slog"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"github.com/spf13/cobra"
+
+	"git.wntrmute.dev/kyle/metacrypt/internal/config"
+	"git.wntrmute.dev/kyle/metacrypt/internal/webserver"
+)
+
+var cfgFile string
+
+var rootCmd = &cobra.Command{
+	Use:   "metacrypt-web",
+	Short: "Metacrypt web UI server",
+	Long:  "Standalone web UI server for Metacrypt. Communicates with the vault over gRPC.",
+	RunE:  run,
+}
+
+func init() {
+	rootCmd.PersistentFlags().StringVar(&cfgFile, "config", "", "config file (default /srv/metacrypt/metacrypt.toml)")
+}
+
+func run(cmd *cobra.Command, args []string) error {
+	logger := slog.New(slog.NewJSONHandler(os.Stdout, nil))
+
+	configPath := cfgFile
+	if configPath == "" {
+		configPath = "/srv/metacrypt/metacrypt.toml"
+	}
+
+	cfg, err := config.Load(configPath)
+	if err != nil {
+		return err
+	}
+
+	if cfg.Web.VaultGRPC == "" {
+		return fmt.Errorf("web.vault_grpc is required in config")
+	}
+
+	ws, err := webserver.New(cfg, logger)
+	if err != nil {
+		return err
+	}
+
+	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	go func() {
+		if err := ws.Start(); err != nil {
+			logger.Error("web server error", "error", err)
+			os.Exit(1)
+		}
+	}()
+
+	<-ctx.Done()
+	logger.Info("shutting down web server")
+	return ws.Shutdown(context.Background())
+}
+
+func main() {
+	if err := rootCmd.Execute(); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}