Sync docs: ARCHITECTURE, PROJECT, PROJECT_PLAN

- ARCHITECTURE.md §12: add mciasdb, mciasgrpcctl, internal/grpcserver,
  proto/, and gen/ to the directory structure diagram
- ARCHITECTURE.md §17: replace buf generate references with protoc;
  the implementation uses protoc + protoc-gen-go + protoc-gen-go-grpc
  invoked via go generate ./... (proto/generate.go)
- PROJECT_PLAN.md §7.1: replace buf.yaml/buf.gen.yaml acceptance
  criteria with the protoc-based go:generate approach actually used
- PROJECT_PLAN.md §7.6: clarify that gen/ is committed to the repo
  (not gitignored); only the binary /mciasgrpcctl is excluded
- PROJECT.md: replace scrypt with Argon2id (the actual algorithm);
  remove the redundant Argon2 suggestion line

ARCHITECTURE.md

@@ -501,19 +501,28 @@ passphrase_env = "MCIAS_MASTER_PASSPHRASE"
 ```
 mcias/
 ├── cmd/
-│   ├── mciassrv/       # server binary entrypoint
+│   ├── mciassrv/       # server binary entrypoint (REST + gRPC dual-stack)
 │   │   └── main.go
-│   └── mciasctl/       # admin CLI entrypoint
+│   ├── mciasctl/       # REST admin CLI
+│   │   └── main.go
+│   ├── mciasdb/        # direct SQLite maintenance tool (Phase 6)
+│   │   └── main.go
+│   └── mciasgrpcctl/   # gRPC admin CLI companion (Phase 7)
 │       └── main.go
 ├── internal/
 │   ├── auth/           # login flow, TOTP verification, account lockout
 │   ├── config/         # config file parsing and validation
 │   ├── crypto/         # key management, AES-GCM helpers, master key derivation
 │   ├── db/             # SQLite access layer (schema, migrations, queries)
+│   ├── grpcserver/     # gRPC handler implementations (Phase 7)
 │   ├── middleware/     # HTTP middleware (auth extraction, logging, rate-limit)
 │   ├── model/          # shared data types (Account, Token, Role, etc.)
 │   ├── server/         # HTTP handlers, router setup
 │   └── token/          # JWT issuance, validation, revocation
+├── proto/
+│   └── mcias/v1/       # Protobuf service definitions (Phase 7)
+├── gen/
+│   └── mcias/v1/       # Generated Go stubs from protoc (committed; Phase 7)
 └── go.mod
 ```
 
@@ -719,11 +728,12 @@ proto/
 
 gen/
 └── mcias/
-    └── v1/                  # Generated Go stubs (buf generate output)
+    └── v1/                  # Generated Go stubs (protoc output)
 ```
 
-Generated code is committed to the repository under `gen/`. `buf generate`
-is idempotent and is re-run via `go generate ./...`.
+Generated code is committed to the repository under `gen/`. The generator
+is invoked via `go generate ./...`, which runs the `protoc` command declared
+in `proto/generate.go` using `protoc-gen-go` and `protoc-gen-go-grpc`.
 
 ### Service Definitions (summary)