Let a module declare a log the controller creates and never removes (ADR 0297)

The issue tracker's history lasts seven days on the events stream and its
bucket fills toward a cap with no warning (issues 501, 502). A module may
now declare `logs`; the controller creates each as a stream on the bus
(create-or-update, never deleted or recreated, reported when undeclared),
issues it to the owner's assignments in their membership, grants the
runtime exactly the append and direct-read subjects, and raises a
condition when any module's bucket or log reaches 75% of its cap, cleared
below 70%.

cmd/mesh-controller/check.go

@@ -179,6 +179,14 @@ func moduleCheckFor(paths []string, longestMachine int, out io.Writer) error {
 			}
 			fmt.Fprintf(out, ", keeps state %s", strings.Join(kept, ", "))
 		}
+		// And the logs it keeps, with their caps (novox/hq ADR 0297).
+		if len(m.Logs) > 0 {
+			kept := make([]string, 0, len(m.Logs))
+			for _, l := range m.Logs {
+				kept = append(kept, fmt.Sprintf("%s (%d MiB)", l.Name, l.Cap()))
+			}
+			fmt.Fprintf(out, ", keeps log %s", strings.Join(kept, ", "))
+		}
 		if len(m.Reads) > 0 {
 			fmt.Fprintf(out, ", reads %s", strings.Join(m.Reads, ", "))
 		}