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/sqlc/queries/projects.sql

@@ -125,3 +125,21 @@ SELECT p.id, p.name, p.description, p.owner_id, p.is_approved, p.created_at, p.u
 FROM projects p
 WHERE p.is_approved = false
 ORDER BY p.created_at DESC;
+
+-- name: ListProjectEnvironments :many
+SELECT e.id, e.name, e.project_id, e.created_at, e.updated_at,
+       (SELECT COUNT(*) FROM services s WHERE s.environment_id = e.id) AS service_count
+FROM environments e
+WHERE e.project_id = $1
+ORDER BY e.created_at;
+
+-- name: GetProjectEnvironmentByName :one
+SELECT id, name, project_id, created_at, updated_at
+FROM environments
+WHERE project_id = $1 AND name = $2;
+
+-- name: DeleteProjectEnvironment :exec
+DELETE FROM environments WHERE id = $1 AND project_id = $2;
+
+-- name: CountEnvironmentServices :one
+SELECT COUNT(*) FROM services WHERE environment_id = $1;