fix(dreaming): align defensive deep-dreaming storage fallback with new "separate" default

Address review feedback on #66412.

`writeDeepDreamingReport` is called with a defensive
`params.config.storage ?? { mode: "inline", ... }` fallback for cases
where the config object is loosely constructed (tests, migrations).
After flipping the unset default to `"separate"` in
`src/memory-host-sdk/dreaming.ts`, this hardcoded `"inline"` fallback
would silently re-introduce the old behavior for any caller that
exercises the fallback branch.

Update the fallback to `"separate"` so all default code paths agree.
The `MemoryDreamingStorageMode` type continues to accept all three
documented modes; this is purely a default-value alignment.

extensions/memory-core/src/dreaming.ts

@@ -615,7 +615,7 @@ export async function runShortTermDreamingPromotionIfTriggered(params: {
         bodyLines: reportLines,
         nowMs: sweepNowMs,
         timezone: params.config.timezone,
-        storage: params.config.storage ?? { mode: "inline", separateReports: false },
+        storage: params.config.storage ?? { mode: "separate", separateReports: false },
       });
       // Generate dream diary narrative from promoted memories.
       if (params.subagent && (candidates.length > 0 || applied.applied > 0)) {