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

PROJECT_PLAN.md

@@ -317,13 +317,14 @@ transport security requirements.
 - `proto/mcias/v1/` directory contains `.proto` files for all service groups:
   `auth.proto`, `token.proto`, `account.proto`, `admin.proto`
 - All RPC methods mirror the REST API surface (see ARCHITECTURE.md §8 and §17)
-- `buf.yaml` / `buf.gen.yaml` configured; `buf generate` produces Go stubs under
-  `gen/mcias/v1/`
+- `proto/generate.go` contains a `//go:generate protoc ...` directive that
+  produces Go stubs under `gen/mcias/v1/` using `protoc-gen-go` and
+  `protoc-gen-go-grpc`
 - Protobuf field conventions: `snake_case` field names, `google.protobuf.Timestamp`
   for all time fields, no credential fields in response messages (same exclusion
   rules as JSON API)
-- `go generate ./...` re-runs `buf generate` idempotently
-- Tests: generated code compiles cleanly; `buf lint` passes with zero warnings
+- `go generate ./...` re-runs `protoc` idempotently
+- Tests: generated code compiles cleanly (`go build ./...` succeeds)
 
 ### Step 7.2: `internal/grpcserver` — gRPC handler implementations
 **Acceptance criteria:**
@@ -379,8 +380,9 @@ transport security requirements.
   interceptor chain, dual-stack operation)
 - README.md updated with gRPC section: enabling gRPC, connecting clients,
   example `grpcurl` invocations
-- `.gitignore` updated to exclude `mciasgrpcctl` binary and `gen/` directory
-  (generated code committed separately or excluded per project convention)
+- `.gitignore` updated to exclude the `mciasgrpcctl` binary (using a
+  root-anchored path `/mciasgrpcctl`); generated code in `gen/` is committed
+  to the repository so that consumers do not need the protoc toolchain
 - `PROGRESS.md` updated to reflect Phase 7 complete
 
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