fix: always return terminal_ids from spawn_uninitialized_terminals

[neumie]

Summary

• Always return terminal_ids in the action response from spawn_uninitialized_terminals, even when no terminals were spawned, so callers can distinguish a completed action from a no-result action
• Add log line for spawn counts to aid debugging

Test plan

• Verify that actions triggering spawn_uninitialized_terminals with zero uninitialized terminals return { "terminal_ids": [] } instead of null
• Verify normal terminal spawning still works and returns populated terminal_ids

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