feat(docker-watcher): phase 11 - frontend embed & SSE

Embed SvelteKit static build in Go binary via go:embed. Event bus
for pub/sub with deploy log, instance status, and deploy status events.
SSE endpoints for real-time streaming. Frontend SSE client with
exponential backoff reconnection. Makefile for build pipeline.
Update Phase 12 auth plan with OAuth2/OIDC support.

Makefile

@@ -0,0 +1,21 @@
+.PHONY: build build-frontend build-backend dev clean
+
+# Build everything: frontend first, then backend (which embeds frontend).
+build: build-frontend build-backend
+
+# Build the SvelteKit frontend to web/build/.
+build-frontend:
+	cd web && npm install && npm run build
+
+# Build the Go binary (embeds web/build/ via go:embed).
+build-backend:
+	go build -o docker-watcher ./cmd/server
+
+# Run in development mode with hot reload.
+# Requires air (go install github.com/air-verse/air@latest).
+dev:
+	air -c .air.toml 2>/dev/null || go run ./cmd/server
+
+# Clean build artifacts.
+clean:
+	rm -rf web/build web/node_modules/.vite docker-watcher