feat(environments): env CRUD, workspace switcher, CLI + MCP parity (#68)

Environment lanes existed as seeded rows (production/preview/development)
with a per-service environment label, but there was no way to list,
create, or delete them. Adds the management surface and the switcher:

- GET /projects/:id/environments with live service counts (sqlc)
- POST /projects/:id/environments — lowercase dns-label names, 1-50
  chars, unique per project (409 on dupe)
- DELETE /environments/:id — refuses while it holds services (409)
- Workspace service list gains env filter chips with counts plus an
  inline "+ env" creator
- CLI: containr environments list|create|delete (--yes on delete);
  MCP: containr_environments_list/create/delete (delete needs confirm)
- OpenAPI: new Environments tag + ProjectEnvironment schema

Live-verified: list counts, name validation, dupe 409, empty delete,
non-empty 409, CLI list.

Generated with [Devin](https://devin.ai)

Co-authored-by: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/cli/commands/environments.go

@@ -0,0 +1,97 @@
+package commands
+
+import (
+	"fmt"
+
+	"github.com/spf13/cobra"
+)
+
+// EnvironmentsCmd manages a project's environment lanes
+// (production/development/preview are seeded; custom names allowed).
+var EnvironmentsCmd = &cobra.Command{
+	Use:     "environments",
+	Aliases: []string{"env", "envs"},
+	Short:   "Manage project environments",
+}
+
+var envListCmd = &cobra.Command{
+	Use:   "list",
+	Short: "List environments in a project",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		project, _ := cmd.Flags().GetString("project")
+		if project == "" {
+			return fmt.Errorf("--project is required")
+		}
+		data, err := c.Do("GET", "/projects/"+project+"/environments", nil)
+		if err != nil {
+			return err
+		}
+		items, err := unwrapList(data, "environments")
+		if err != nil {
+			return err
+		}
+		rows := make([][]string, 0, len(items))
+		for _, e := range items {
+			rows = append(rows, []string{
+				str(e, "id"), str(e, "name"), str(e, "service_count"), relTime(e, "created_at"),
+			})
+		}
+		printRows(data, []string{"ID", "NAME", "SERVICES", "CREATED"}, rows)
+		return nil
+	},
+}
+
+var envCreateCmd = &cobra.Command{
+	Use:   "create <name>",
+	Short: "Create an environment in a project",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		project, _ := cmd.Flags().GetString("project")
+		if project == "" {
+			return fmt.Errorf("--project is required")
+		}
+		data, err := c.Do("POST", "/projects/"+project+"/environments", map[string]interface{}{
+			"name": args[0],
+		})
+		if err != nil {
+			return err
+		}
+		PrintRaw(data)
+		return nil
+	},
+}
+
+var envDeleteCmd = &cobra.Command{
+	Use:   "delete <id>",
+	Short: "Delete an empty environment",
+	Args:  cobra.ExactArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if !Confirm("Delete environment " + args[0] + "?") {
+			return &APIError{Message: "aborted (pass --yes to skip confirmation)", ExitCode: ExitError}
+		}
+		c, err := client()
+		if err != nil {
+			return err
+		}
+		_, err = c.Do("DELETE", "/environments/"+args[0], nil)
+		if err != nil {
+			return err
+		}
+		fmt.Println("Environment deleted")
+		return nil
+	},
+}
+
+func init() {
+	envListCmd.Flags().String("project", "", "project ID (required)")
+	envCreateCmd.Flags().String("project", "", "project ID (required)")
+	EnvironmentsCmd.AddCommand(envListCmd, envCreateCmd, envDeleteCmd)
+}