Cover every cell of the delivery routing table

Table-driven tests for all four severity bands crossed with present and away,
both as the pure table and end to end through the dispatcher. Three tests are
written to DESIGN.md and skipped because the code does not keep the claim: the
care-away drop is recorded nowhere, and the minimal body is enforced per-sink
rather than by the dispatcher. Also gofmt'd dispatcher_test.go.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CGeSZxh1DCtRxmFVSYVGvJ

internal/delivery/dispatcher_test.go

@@ -639,11 +639,11 @@ func TestDispatchRecurringReminderReschedules(t *testing.T) {
 // ----------------------------- durable outbox --------------------------------
 
 type outboxAttempt struct {
-	kind, rule       string
-	reminderID       int64
-	channel, hash    string
-	status           string
-	begunAt, doneAt  time.Time
+	kind, rule      string
+	reminderID      int64
+	channel, hash   string
+	status          string
+	begunAt, doneAt time.Time
 }
 
 // fakeOutbox — an in-memory Outbox that also lets a test simulate a crash