Migrate gRPC server to mcdsl grpcserver package

Replace metacrypt's hand-rolled gRPC interceptor chain with the mcdsl
grpcserver package, which provides TLS setup, logging, and method-map
auth (public/auth-required/admin-required) out of the box.

Metacrypt-specific interceptors are preserved as hooks:
- sealInterceptor runs as a PreInterceptor (before logging/auth)
- auditInterceptor runs as a PostInterceptor (after auth)

The three legacy method maps (seal/auth/admin) are restructured into
mcdsl's MethodMap (Public/AuthRequired/AdminRequired) plus a separate
seal-required map for the PreInterceptor. Token context is now stored
via mcdsl/auth.ContextWithTokenInfo instead of a package-local key.

Bumps mcdsl from v1.0.0 to v1.0.1 (adds PreInterceptors/PostInterceptors
to grpcserver.Options).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

go.mod

@@ -4,7 +4,7 @@ go 1.25.7
 
 require (
 	git.wntrmute.dev/kyle/goutils v1.21.0
-	git.wntrmute.dev/kyle/mcdsl v1.0.0
+	git.wntrmute.dev/kyle/mcdsl v1.0.1
 	github.com/go-chi/chi/v5 v5.2.5
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0