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>

internal/grpcserver/pki.go

@@ -0,0 +1,81 @@
+package grpcserver
+
+import (
+	"context"
+	"errors"
+
+	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/status"
+
+	pb "git.wntrmute.dev/kyle/metacrypt/gen/metacrypt/v1"
+	"git.wntrmute.dev/kyle/metacrypt/internal/engine"
+	"git.wntrmute.dev/kyle/metacrypt/internal/engine/ca"
+)
+
+type pkiServer struct {
+	pb.UnimplementedPKIServiceServer
+	s *GRPCServer
+}
+
+func (ps *pkiServer) GetRootCert(_ context.Context, req *pb.GetRootCertRequest) (*pb.GetRootCertResponse, error) {
+	caEng, err := ps.getCAEngine(req.Mount)
+	if err != nil {
+		return nil, err
+	}
+	certPEM, err := caEng.GetRootCertPEM()
+	if err != nil {
+		return nil, status.Error(codes.Unavailable, "sealed")
+	}
+	return &pb.GetRootCertResponse{CertPem: certPEM}, nil
+}
+
+func (ps *pkiServer) GetChain(_ context.Context, req *pb.GetChainRequest) (*pb.GetChainResponse, error) {
+	if req.Issuer == "" {
+		return nil, status.Error(codes.InvalidArgument, "issuer is required")
+	}
+	caEng, err := ps.getCAEngine(req.Mount)
+	if err != nil {
+		return nil, err
+	}
+	chainPEM, err := caEng.GetChainPEM(req.Issuer)
+	if err != nil {
+		if errors.Is(err, ca.ErrIssuerNotFound) {
+			return nil, status.Error(codes.NotFound, "issuer not found")
+		}
+		return nil, status.Error(codes.Unavailable, "sealed")
+	}
+	return &pb.GetChainResponse{ChainPem: chainPEM}, nil
+}
+
+func (ps *pkiServer) GetIssuerCert(_ context.Context, req *pb.GetIssuerCertRequest) (*pb.GetIssuerCertResponse, error) {
+	if req.Issuer == "" {
+		return nil, status.Error(codes.InvalidArgument, "issuer is required")
+	}
+	caEng, err := ps.getCAEngine(req.Mount)
+	if err != nil {
+		return nil, err
+	}
+	certPEM, err := caEng.GetIssuerCertPEM(req.Issuer)
+	if err != nil {
+		if errors.Is(err, ca.ErrIssuerNotFound) {
+			return nil, status.Error(codes.NotFound, "issuer not found")
+		}
+		return nil, status.Error(codes.Unavailable, "sealed")
+	}
+	return &pb.GetIssuerCertResponse{CertPem: certPEM}, nil
+}
+
+func (ps *pkiServer) getCAEngine(mountName string) (*ca.CAEngine, error) {
+	mount, err := ps.s.engines.GetMount(mountName)
+	if err != nil {
+		return nil, status.Error(codes.NotFound, err.Error())
+	}
+	if mount.Type != engine.EngineTypeCA {
+		return nil, status.Error(codes.NotFound, "mount is not a CA engine")
+	}
+	caEng, ok := mount.Engine.(*ca.CAEngine)
+	if !ok {
+		return nil, status.Error(codes.NotFound, "mount is not a CA engine")
+	}
+	return caEng, nil
+}