feat(messaging): route messages to live runs via pi steer

Incoming messages (human → agent, agent → agent, channel broadcast)
persisted to the inbox and were only projected into the recipient's
transcript on the next `prepareRun`. When the recipient was already
running, every message waited for the next wake — a Slack-like
system operating at heartbeat cadence, not in real time.

`RuntimeMessageInjector` closes the gap: it looks up the recipient's
active run through `RuntimeBridge.findActiveRunForAgent`, projects
the persisted `AgentMessageRecord` via the existing inbox-projection
helper, and posts a `steer-run` ParentMessage into the worker. The
worker's runner enqueues the projection on the Agent's steering
queue; pi drains it at the next turn boundary and emits the usual
`message_end` → `persistMessage` sequence, so the session store
shadow is preserved without double-writing.

`dispatchAgentMessage` gains an optional `injectRuntimeMessage` hook
used by every API-side dispatch. Injection succeeds → we mark the
inbox row delivered and skip `wakeAgentIfPossible`. Injection fails
(no active run) → the legacy inbox + wake path still fires, so
sleeping agents continue to receive their messages on the next turn.

The injector is owned by the service graph alongside `workerService`
and `piRuntimeRef`, which gives it both the worker postMessage
channel and the RuntimeBridge active-run map without additional
coupling. Internal dispatch call sites (sweepStaleReviews,
automation actions) leave the hook unset; those system messages
target idle agents by design and do not need the runtime path.

src/main/api-server/routes-messages.ts

@@ -109,6 +109,7 @@ export function registerMessageRoutes(server: AgentApiServer) {
           if (!agentId) return null;
           return onWakeAgent(agentId, cid, trigger);
         },
+        injectRuntimeMessage: server.callbacks.injectRuntimeMessage,
         onHumanMessage: server.callbacks.onHumanMessage,
       },
       parsed.data,