Skip cleanly when channel-target resolution fails

`dispatchAgentMessage` requires a `channelTargetId` for `department`
and `project` channels, but the default "Notify department on task
completion" rule is agent-agnostic — it has to derive the target at
fire time. Single-agent companies and any sender without a
`department` produced a WARN every run completion that read like a
real failure and made the log tail look like the system was broken.

The action handler now treats "channel needs a target and we
couldn't resolve one" as "no recipient available" and skips with an
INFO line. The dispatcher is no longer asked to validate an input we
already know is incomplete, and the operator stops seeing
`CHANNEL_TARGET_REQUIRED` rejections during routine completions.

src/main/automation/automation-actions.ts

@@ -154,6 +154,21 @@ export function executeAutomationAction(
           channelTargetId = null;
         }
       }
+      // `dispatchAgentMessage` rejects department / project messages
+      // that arrive without a channel target. The default rule
+      // "Notify department on task completion" is agent-agnostic
+      // (the operator may not have a department per agent), so a
+      // single-person company or any agent without a department
+      // routinely lands here. Treat the missing target as "no
+      // recipients available" and skip — the previous behaviour
+      // logged a noisy WARN that looked like a real failure.
+      const channelNeedsTarget = channel === "department" || channel === "project";
+      if (channelNeedsTarget && !channelTargetId) {
+        logger.info(
+          `[automation] Skipping rule "${rule.name}" — no ${channel} channel target available for sender ${fromAgentId}`,
+        );
+        break;
+      }
       const dispatchResult = dispatchAgentMessage(
         { db, emitEvent, publishDomainChanged, wakeAgentIfPossible },
         {