fleet: send log counters in heartbeats and pull the text on demand

Heartbeats carry per-level counts, the most frequent log types (a stable hash of the message) and the newest id, no text. The node keeps its last 2048 lines; moshiro.logs.fetch lets the backend pull them. The log page pulls when it is open, and the backend pulls warnings and errors once a minute after a node reports an error.

web/shared/api/schema.ts

@@ -508,7 +508,7 @@ export interface paths {
             path?: never;
             cookie?: never;
         };
-        /** Recent runtime logs of a node */
+        /** Recent runtime logs of a node: pulled from the node when it is online, otherwise what the backend kept */
         get: operations["node_runtime_logs"];
         put?: never;
         post?: never;