Implement Phase 7: gRPC dual-stack interface

- proto/mcias/v1/: AdminService, AuthService, TokenService,
  AccountService, CredentialService; generated Go stubs in gen/
- internal/grpcserver: full handler implementations sharing all
  business logic (auth, token, db, crypto) with REST server;
  interceptor chain: logging -> auth (JWT alg-first + revocation) ->
  rate-limit (token bucket, 10 req/s, burst 10, per-IP)
- internal/config: optional grpc_addr field in [server] section
- cmd/mciassrv: dual-stack startup; gRPC/TLS listener on grpc_addr
  when configured; graceful shutdown of both servers in 15s window
- cmd/mciasgrpcctl: companion gRPC CLI mirroring mciasctl commands
  (health, pubkey, account, role, token, pgcreds) using TLS with
  optional custom CA cert
- internal/grpcserver/grpcserver_test.go: 20 tests via bufconn covering
  public RPCs, auth interceptor (no token, invalid, revoked -> 401),
  non-admin -> 403, Login/Logout/RenewToken/ValidateToken flows,
  AccountService CRUD, SetPGCreds/GetPGCreds AES-GCM round-trip,
  credential fields absent from all responses
Security:
  JWT validation path identical to REST: alg header checked before
  signature, alg:none rejected, revocation table checked after sig.
  Authorization metadata value never logged by any interceptor.
  Credential fields (PasswordHash, TOTPSecret*, PGPassword) absent from
  all proto response messages — enforced by proto design and confirmed
  by test TestCredentialFieldsAbsentFromAccountResponse.
  Login dummy-Argon2 timing guard preserves timing uniformity for
  unknown users (same as REST handleLogin).
  TLS required at listener level; cmd/mciassrv uses
  credentials.NewServerTLSFromFile; no h2c offered.
137 tests pass, zero race conditions (go test -race ./...)

proto/mcias/v1/auth.proto

@@ -0,0 +1,99 @@
+// AuthService: login, logout, token renewal, and TOTP management.
+syntax = "proto3";
+
+package mcias.v1;
+
+option go_package = "git.wntrmute.dev/kyle/mcias/gen/mcias/v1;mciasv1";
+
+import "google/protobuf/timestamp.proto";
+
+// --- Login ---
+
+// LoginRequest carries username/password and an optional TOTP code.
+// Security: never logged; password and totp_code must not appear in audit logs.
+message LoginRequest {
+  string username  = 1;
+  string password  = 2;  // security: never logged or stored
+  string totp_code = 3;  // optional; required if TOTP enrolled
+}
+
+// LoginResponse returns the signed JWT and its expiry time.
+// Security: token is a bearer credential; the caller must protect it.
+message LoginResponse {
+  string token = 1;
+  google.protobuf.Timestamp expires_at = 2;
+}
+
+// --- Logout ---
+
+// LogoutRequest carries no body; the token is extracted from gRPC metadata.
+message LogoutRequest {}
+
+// LogoutResponse confirms the token has been revoked.
+message LogoutResponse {}
+
+// --- Token renewal ---
+
+// RenewTokenRequest carries no body; the existing token is in metadata.
+message RenewTokenRequest {}
+
+// RenewTokenResponse returns a new JWT with a fresh expiry.
+message RenewTokenResponse {
+  string token = 1;
+  google.protobuf.Timestamp expires_at = 2;
+}
+
+// --- TOTP enrollment ---
+
+// EnrollTOTPRequest carries no body; the acting account is from the JWT.
+message EnrollTOTPRequest {}
+
+// EnrollTOTPResponse returns the TOTP secret and otpauth URI for display.
+// Security: the secret is shown once; it is stored only in encrypted form.
+message EnrollTOTPResponse {
+  string secret      = 1;  // base32-encoded; display once, then discard
+  string otpauth_uri = 2;
+}
+
+// ConfirmTOTPRequest carries the TOTP code to confirm enrollment.
+message ConfirmTOTPRequest {
+  string code = 1;
+}
+
+// ConfirmTOTPResponse confirms TOTP enrollment is complete.
+message ConfirmTOTPResponse {}
+
+// RemoveTOTPRequest carries the target account ID (admin only).
+message RemoveTOTPRequest {
+  string account_id = 1;  // UUID of the account to remove TOTP from
+}
+
+// RemoveTOTPResponse confirms removal.
+message RemoveTOTPResponse {}
+
+// AuthService handles all authentication flows.
+service AuthService {
+  // Login authenticates with username+password (+optional TOTP) and returns a JWT.
+  // Public RPC — no auth required.
+  rpc Login(LoginRequest) returns (LoginResponse);
+
+  // Logout revokes the caller's current token.
+  // Requires: valid JWT in metadata.
+  rpc Logout(LogoutRequest) returns (LogoutResponse);
+
+  // RenewToken exchanges the caller's token for a fresh one.
+  // Requires: valid JWT in metadata.
+  rpc RenewToken(RenewTokenRequest) returns (RenewTokenResponse);
+
+  // EnrollTOTP begins TOTP enrollment for the calling account.
+  // Requires: valid JWT in metadata.
+  rpc EnrollTOTP(EnrollTOTPRequest) returns (EnrollTOTPResponse);
+
+  // ConfirmTOTP confirms TOTP enrollment with a code from the authenticator app.
+  // Requires: valid JWT in metadata.
+  rpc ConfirmTOTP(ConfirmTOTPRequest) returns (ConfirmTOTPResponse);
+
+  // RemoveTOTP removes TOTP from an account (admin only).
+  // Requires: admin JWT in metadata.
+  rpc RemoveTOTP(RemoveTOTPRequest) returns (RemoveTOTPResponse);
+}