BDD DSL: Group required environment-variable checks

[sbaum1994]

Why

Feature backgrounds contain about 60 individual environment-variable prerequisite steps. The variable names matter, but repeating the sentence for every name makes prerequisites harder to scan.

Scope

Add a table-driven step that asserts all named environment variables are non-empty. Keep every required variable visible in the feature file and report the specific missing variable.

Acceptance criteria

• Add the step to the documented DSL catalog.
• Validate the table shape and reject empty names.
• Report the exact missing environment variable.
• Migrate existing prerequisite groups without changing the required variables.
• Pass affected wiring tests and live feature tests.

Parent: #858