chore: remove dead v3 prototype code from embedded-cluster v2

The v3 prototype has been abandoned and moved to a separate repository.
This cleanup removes all dead v3-specific code, environment variable gates
(ENABLE_V3), and v3-only features from the v2 production codebase.

Deleted files:
- cmd/installer/cli/install_v3.go and tests
- cmd/installer/cli/headless/install/* (entire directory)
- tests/dryrun/v3_*_test.go (4 files)
- .github/workflows/v3-e2e.yaml
- e2e/kots-release-install-v3/* and upgrade-v3/*
- e2e/licenses/ci-v3.yaml
- pkg-new/k0s/mock.go, pkg-new/upgrade/mock.go

Key changes:
- Remove ENABLE_V3 env var gates from install, upgrade, version commands
- Simplify KotsadmNamespace to always return 'kotsadm'
- Simplify EmbeddedClusterLogsPath to use static v2 path
- Remove headless install orchestrator and v3 install flow
- Remove dead code from pkg-new/* packages
- Update Makefile to always use v2 release directories
- Update tests to match v2-only behavior
- dagger: remove InstallHeadless, E2eRunHeadless helpers

Build and tests pass.

Author: kriscoleman

.github/workflows/v3-e2e.yaml

@@ -181,23 +181,17 @@ output/bin/embedded-cluster-release-builder:
 	mkdir -p output/bin
 	CGO_ENABLED=0 go build -o output/bin/embedded-cluster-release-builder e2e/embedded-cluster-release-builder/main.go
 
-.PHONY: e2e-v3-initial-release
-e2e-v3-initial-release: export ARCH = amd64
-e2e-v3-initial-release: export UPLOAD_BINARIES = 1
-e2e-v3-initial-release: export ENABLE_V3 = 1
-e2e-v3-initial-release: initial-release
-
 .PHONY: initial-release
 initial-release: RANDOM_STRING = $(call random-string)
 initial-release: export EC_VERSION ?= $(VERSION)-$(RANDOM_STRING)
 initial-release: export APP_VERSION ?= appver-dev-$(RANDOM_STRING)
-initial-release: export RELEASE_YAML_DIR = $(if $(filter 1,$(ENABLE_V3)),e2e/kots-release-install-v3,e2e/kots-release-install)
+initial-release: export RELEASE_YAML_DIR = e2e/kots-release-install
 initial-release: check-env-EC_VERSION check-env-APP_VERSION
 	UPLOAD_BINARIES=$(if $(UPLOAD_BINARIES),$(UPLOAD_BINARIES),0) \
 		./scripts/build-and-release.sh
 
 .PHONY: rebuild-release
-rebuild-release: export RELEASE_YAML_DIR = $(if $(filter 1,$(ENABLE_V3)),e2e/kots-release-install-v3,e2e/kots-release-install)
+rebuild-release: export RELEASE_YAML_DIR = e2e/kots-release-install
 rebuild-release: check-env-EC_VERSION check-env-APP_VERSION
 	UPLOAD_BINARIES=$(if $(UPLOAD_BINARIES),$(UPLOAD_BINARIES),0) \
 	SKIP_RELEASE=1 \
@@ -207,7 +201,7 @@ rebuild-release: check-env-EC_VERSION check-env-APP_VERSION
 upgrade-release: RANDOM_STRING = $(call random-string)
 upgrade-release: export EC_VERSION ?= $(VERSION)-upgrade-$(RANDOM_STRING)
 upgrade-release: export APP_VERSION ?= appver-dev-upgrade-$(RANDOM_STRING)
-upgrade-release: export RELEASE_YAML_DIR = $(if $(filter 1,$(ENABLE_V3)),e2e/kots-release-upgrade-v3,e2e/kots-release-upgrade)
+upgrade-release: export RELEASE_YAML_DIR = e2e/kots-release-upgrade
 upgrade-release: check-env-EC_VERSION check-env-APP_VERSION
 	UPLOAD_BINARIES=$(if $(UPLOAD_BINARIES),$(UPLOAD_BINARIES),1) \
 		./scripts/build-and-release.sh
@@ -349,31 +343,20 @@ create-node%: DISTRO = debian-bookworm
 create-node%: NODE_PORT = 30000
 create-node%: MANAGER_NODE_PORT = 30080
 create-node%: K0S_DATA_DIR = /var/lib/embedded-cluster/k0s
-create-node%: K0S_DATA_DIR_V3 = $(shell \
-	if [ -n "$(REPLICATED_APP)" ]; then \
-		echo "/var/lib/$(shell echo '$(REPLICATED_APP)' | tr '[:upper:]' '[:lower:]' | sed 's/[^a-z0-9-]/-/g')/k0s"; \
-	else \
-		echo "/var/lib/embedded-cluster-smoke-test-staging-app/k0s"; \
-	fi)
-create-node%: ENABLE_V3 = 0
 create-node%:
-	@echo "Mounting data directories:"
-	@echo "  v2: $(K0S_DATA_DIR)"
-	@echo "  v3: $(K0S_DATA_DIR_V3)"
+	@echo "Mounting data directory: $(K0S_DATA_DIR)"
 	@docker run -d \
 		--name node$* \
 		--hostname node$* \
 		--privileged \
 		--restart=unless-stopped \
 		-v $(K0S_DATA_DIR) \
-		-v $(K0S_DATA_DIR_V3) \
 		-v $(shell pwd):/replicatedhq/embedded-cluster \
 		-v $(shell dirname $(shell pwd))/kots:/replicatedhq/kots \
 		$(if $(filter node0,node$*),-p $(NODE_PORT):$(NODE_PORT)) \
 		$(if $(filter node0,node$*),-p $(MANAGER_NODE_PORT):$(MANAGER_NODE_PORT)) \
 		$(if $(filter node0,node$*),-p 30003:30003) \
 		-e EC_PUBLIC_ADDRESS=localhost \
-		-e ENABLE_V3=$(ENABLE_V3) \
 		replicated/ec-distro:$(DISTRO)
 
 	@$(MAKE) ssh-node$*