Stacked on #2269 (back-nav scaffolding) plus the Telegram, Slack, and
Teams PRs. They share the same scaffolding file from #2269 — they
don't compile without it, so they have to stack.
Signal had no user-facing prompt before the install kicked off, so
there was nothing to attach a Back option to. This adds a brief "Set
up Signal" info card (what's about to happen, no new phone number
needed) followed by a Continue/Back brightSelect. The card serves
double duty — context for the install plus the Back gate.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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