Open every explanation with what the operator needs to do, and offer the answers

The operator could not tell from a notification whether to act, and was told to
have an agent do it. Each condition now says "Nothing for you to do." or
"Needs you:" with one thing they can do themselves, and carries the actions the
operator channel performs when chosen (hq ADR 0253).

internal/conditions/condition.go

@@ -134,6 +134,10 @@ type Condition struct {
 	Headline    string `json:"headline"`
 	Explanation string `json:"explanation"`
 	Resolved    string `json:"resolved"`
+	// Needs is what the operator does about it, one sentence; empty when nothing (the explanation then
+	// opens "Nothing for you to do."). Actions are the answers a notification offers (plain.go).
+	Needs   string   `json:"needs"`
+	Actions []Action `json:"actions"`
 	// Evidence is the newest observations, at most KeptEvidence, newest first.
 	Evidence []Evidence `json:"evidence"`
 	// Source is the signals-table row, probe or event that raised it: `S1`, `D3`, `provisioner.failing`.
@@ -187,6 +191,8 @@ type Observation struct {
 	Headline    string
 	Explanation string
 	Resolved    string
+	Needs       string
+	Actions     []Action
 	// Said is this observation's evidence, in the mesh's words; Summary when empty. **Detail goes
 	// here, never in Summary**: an address, a socket's error, a path or a name with its domain is
 	// kept in the condition's evidence, which stays inside the mesh. The summary leaves it — to the