Add Go project scaffold for Wails v2 SSH/Telnet/RAW TCP client

- go.mod with Wails v2.9.2, x/crypto, go-sqlite3, go-keyring, uuid
- cmd/app/main.go: Wails entry point (Nexus Terminal, 1400x900, #1a1a2e)
- internal/app/app.go: lifecycle (Startup/Shutdown/DomReady)
- internal/models/models.go: full model definitions (Profile, SSHConfig,
  TelnetConfig, RAWConfig, SessionInfo, KnownHost, AppPreferences, etc.)
- internal/models/defaults.go: default values and NewProfile factory
- internal/validation/validation.go: thorough field-level validation
- frontend/embed.go: embedded frontend assets
- Updated existing storage, secrets, config to match new model structure

Makefile

@@ -0,0 +1,59 @@
+.PHONY: all build dev clean test test-cover lint install deps frontend-deps run package help
+
+# Default target
+all: build
+
+# Install all dependencies
+deps: frontend-deps
+	go mod download
+
+# Install frontend dependencies
+frontend-deps:
+	cd frontend && npm install
+
+# Development mode with hot reload
+dev: deps
+	wails dev
+
+# Production build
+build: deps
+	wails build
+
+# Run tests
+test:
+	go test ./... -v -count=1
+
+# Run tests with coverage
+test-cover:
+	go test ./... -v -count=1 -coverprofile=coverage.out
+	go tool cover -html=coverage.out -o coverage.html
+
+# Clean build artefacts
+clean:
+	rm -rf build/bin
+	rm -rf frontend/node_modules
+	rm -rf frontend/src/js/lib
+	rm -rf frontend/src/css/lib
+	go clean -testcache
+
+# Lint (requires golangci-lint)
+lint:
+	golangci-lint run ./...
+
+# Package for distribution
+package: build
+	@echo "Binary built at build/bin/"
+
+# Help
+help:
+	@echo "Nexus Terminal — Build Targets"
+	@echo ""
+	@echo "  make deps          — Install all dependencies"
+	@echo "  make dev           — Run in development mode with hot reload"
+	@echo "  make build         — Production build"
+	@echo "  make test          — Run tests"
+	@echo "  make test-cover    — Run tests with coverage report"
+	@echo "  make clean         — Clean build artefacts"
+	@echo "  make lint          — Run linter (requires golangci-lint)"
+	@echo "  make package       — Build and package for distribution"
+	@echo "  make help          — Show this help"