docs(dashboard-agent): state what makes a watch fire, not how to reproduce it

The guidebook was a walkthrough of the scenario kit: a command, some clicks, and
the sentence that came back. It is now a reference of conditions, derived from
the checks rather than from the old prose, so a reader can predict an outcome
without running anything.

Corrects, among others: the queue Investigate rule (a zero or unset concurrency
limit is never saturation), the run-panel Investigate rule (it needs an error
block as well as a failed status), the claim that a backed-up queue never offers
an investigate chip (the page registry offers both), and the claim that every
wake is an LLM call (only attention outcomes and consented investigations are).

Author: kathiekiwi