Add architecture docs, fix gRPC/REST API parity, project conventions

- Add ARCHITECTURE.md with full system specification
- Add Project Structure and API Sync Rule to CLAUDE.md; ignore srv/
- Fix engine.proto MountRequest missing config field
- Add pki.proto PKIService to match unauthenticated REST PKI routes

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Makefile

@@ -1,11 +1,11 @@
-.PHONY: build test vet clean docker all
-
-build:
-	go build ./...
+.PHONY: build test vet clean docker all devserver
 
 metacrypt:
 	go build -trimpath -ldflags="-s -w" -o metacrypt ./cmd/metacrypt
 
+build:
+	go build ./...
+
 test:
 	go test ./...
 
@@ -21,4 +21,7 @@ docker:
 docker-compose:
 	docker compose -f deploy/docker/docker-compose.yml up --build
 
+devserver: metacrypt
+	./metacrypt server --config srv/metacrypt.toml
+
 all: vet test metacrypt