The Test Connection action invoked a real single-turn agent run to verify
runtime connectivity. In practice it was expensive (reuses none of the
normal task exec env, so it also gave misleading results) and low value —
daemon heartbeat + Online status already covers the "is the runtime
alive" question. Dropping the whole end-to-end probe path:
- deletes server handler and in-memory PingStore
- drops pending_ping from the heartbeat response and daemon poll loop
- removes daemon.handlePing, PendingPing, ReportPingResult
- removes the CLI `multica runtime ping` command
- removes the PingSection UI block and RuntimePing types / api methods