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/mcpserver/server.go

@@ -50,6 +50,11 @@ func init() {
 	register(spec{"containr_projects_create", "Create a project. Args: name (required), description.", "POST", "/projects", nil, []string{"name", "description"}, false})
 	register(spec{"containr_projects_delete", "Delete a project and all its services. Requires confirm:true.", "DELETE", "/projects/{id}", []string{"id"}, nil, true})
 
+	// Environments
+	register(spec{"containr_environments_list", "List environments in a project with service counts", "GET", "/projects/{id}/environments", []string{"id"}, nil, false})
+	register(spec{"containr_environments_create", "Create an environment. Args: name (required — lowercase alphanumeric with dashes, 1-50 chars).", "POST", "/projects/{id}/environments", []string{"id"}, []string{"name"}, false})
+	register(spec{"containr_environments_delete", "Delete an empty environment. Requires confirm:true.", "DELETE", "/environments/{id}", []string{"id"}, nil, true})
+
 	// Services
 	register(spec{"containr_services_list", "List services in a project", "GET", "/projects/{project_id}/services", []string{"project_id"}, nil, false})
 	register(spec{"containr_services_get", "Get a service by id", "GET", "/services/{id}", []string{"id"}, nil, false})