fix(onboarding): make continue-prompt consistent with other decision prompts

The 'Continue where you left off?' prompt used a 10s AUTO_ADVANCE timer and a
plain [Y]/[N] key prompt, while the import and telemetry-consent prompts use a
60s DECISION_TIMEOUT and a highlightable left/right Yes/No selector. This was
inconsistent and gave the user only 10s to react to a meaningful decision.

- Move ContinuePrompt onto DECISION_TIMEOUT (60s) via decision_seconds_remaining
  / decision_timed_out (it no longer participates in auto_advance, which now
  only drives the TranscriptPick auto-select).
- Add yes_highlighted to the phase + welcome-kind, default Yes.
- Drive it with Left/h, Right/l, Up/Down/k/j/Tab toggle, y/n commit, Enter/Space
  commit highlighted, matching the telemetry-consent handler.
- Render the same highlightable Yes/No selector and movement hint.
- Update unit tests and golden assertions.