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.sum

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+git.wntrmute.dev/kyle/mcdsl v1.0.1/go.mod h1:wo0tGfUAxci3XnOe4/rFmR0RjUElKdYUazc+Np986sg=
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