deploy: Deploy the registry to GCP (#255)

Adds the Pulumi code to:
- Deploy the registry (and associated services e.g. mongodb) to Google
Cloud Platform (GCP), on top of Google Kubernetes Engine (GKE)
- Sets up proper environments and secrets management
- Uses the real container image, now that it's published in #225. At the
moment attached to latest, we might want to pin the version later (or
perhaps always use `latest` in staging, and pin prod)
- Uses real domains (`staging.registry.modelcontextprotocol.io`) rather
than examples (``)

## Motivation and Context

Setting up infrastructure to deploy it. I set something up in Azure in
#227, although not super robust (e.g. no service accounts etc.). Think
we will use GCP as:
- the maintainers have experience with GCP, but none with Azure
- costs are quite low, and Anthropic is happy to cover them in the short
term
- means we only have to maintain one login system (just Google Cloud
Identity), not two (Google Workspace + Azure)

## How Has This Been Tested?

Deployed this to a staging and production cluster. Try it yourself at:

```bash
curl -H "Host: staging.registry.modelcontextprotocol.io" -k https://35.222.36.75/v0/ping
```

(will be sorting out domains very soon)

## Breaking Changes

NA - just adds support for GCP deployment

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

## Additional context
<!-- Add any other context, implementation notes, or design decisions
-->

Expected follow-ups:
- GitHub Action setup to deploy things to the cluster from GitHub, to
avoid gatekeeping to just the people with the secrets.

deploy/Makefile

@@ -1,47 +1,31 @@
-.PHONY: help init preview deploy destroy clean dev-init prod-init dev-deploy prod-deploy
+.PHONY: help build local-preview local-up staging-preview staging-up prod-preview prod-up
 
+# Default target
 help: ## Show this help message
-	@echo "Usage: make [target]"
-	@echo ""
-	@echo "Targets:"
-	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | awk 'BEGIN {FS = ":.*?## "}; {printf "  %-15s %s\n", $$1, $$2}'
+	@echo "Available targets:"
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "  %-20s %s\n", $$1, $$2}'
 
-init: ## Initialize Pulumi stack
-	pulumi stack init
+# Build the Go binary
+build: ## Build the Pulumi Go program
+	go build
 
-preview: ## Preview infrastructure changes
-	pulumi preview
+# Local stack commands
+local-preview: build ## Preview local infrastructure changes
+	PULUMI_CONFIG_PASSPHRASE="" pulumi preview --stack local
 
-deploy: ## Deploy infrastructure
-	pulumi up --yes
+local-up: build ## Deploy local infrastructure
+	PULUMI_CONFIG_PASSPHRASE="" pulumi up --yes --stack local
 
-destroy: ## Destroy infrastructure
-	pulumi destroy --yes
+# Staging stack commands
+staging-preview: build ## Preview staging infrastructure changes
+	PULUMI_CONFIG_PASSPHRASE_FILE=passphrase.staging.txt pulumi preview --stack gcpStaging
 
-clean: ## Clean up temporary files
-	rm -rf .pulumi/
-	rm -f Pulumi.*.yaml.bak
+staging-up: build ## Deploy staging infrastructure
+	PULUMI_CONFIG_PASSPHRASE_FILE=passphrase.staging.txt pulumi up --yes --stack gcpStaging
 
-dev-init: ## Initialize development stack
-	pulumi stack init dev
-	pulumi stack select dev
+# Production stack commands
+prod-preview: build ## Preview production infrastructure changes
+	PULUMI_CONFIG_PASSPHRASE_FILE=passphrase.prod.txt pulumi preview --stack gcpProd
 
-prod-init: ## Initialize production stack
-	pulumi stack init prod
-	pulumi stack select prod
-
-dev-deploy: ## Deploy to development environment
-	pulumi stack select dev
-	pulumi up --yes
-
-prod-deploy: ## Deploy to production environment
-	pulumi stack select prod
-	pulumi up --yes
-
-dev-destroy: ## Destroy development environment
-	pulumi stack select dev
-	pulumi destroy --yes
-
-prod-destroy: ## Destroy production environment
-	pulumi stack select prod
-	pulumi destroy --yes
+prod-up: build ## Deploy production infrastructure
+	PULUMI_CONFIG_PASSPHRASE_FILE=passphrase.prod.txt pulumi up --yes --stack gcpProd