feat(inbox): match Cloud signal card wording and structure

- Consistent SignalCardHeader: colored dot + "Product · Type" + Weight badge
- Source-specific cards: error tracking (fingerprint), GitHub (labels, link),
  Zendesk (priority/status/tags), LLM analytics (model/provider/trace)
- Cloud-exact source line labels and product colors
- Type guards dispatch signals to correct card variant

Author: Twixes