Drop the second confirmation after picking a model in balade generate

[PhilDL]

What to build

Remove the confirmation prompt that follows the interactive model picker in balade generate. Selecting a model in the picker is already an explicit choice; asking "Generate with provider/model?" immediately after costs a keystroke on every run and adds no information — the billing caveat is already shown in the picker option description and in the announcement line.

Today the confirm exists only on the picker path (src/generate/command.ts, selectAuthorModel): an exact --provider/--model pair and a reused saved preference both skip it already, so removing it also makes the three selection paths consistent.

Acceptance criteria

• Choosing a model in the picker starts generation directly; no second confirmation prompt.
• The chosen model is still announced (provider, model, billing caveat where relevant) before the first authoring turn.
• The selection is still saved as the default, matching the recorded preference behavior in DECISIONS.md.
• Cancelling out of the picker itself (quit) still exits with "Generation cancelled." and no preference write.
• Tests covering the picker path no longer expect a confirm step.

Blocked by

None — can start immediately.