fix: keep async music delivery agent-mediated (#75335)

Keep async music generation completions on the requester-session wake path even when direct-send completion is enabled.

Also aligns config help, generated schema text, public docs, and the changelog so tools.media.asyncCompletion.directSend no longer claims to direct-send music completions.

Verification:
- pnpm test src/agents/tools/music-generate-background.test.ts src/agents/tools/video-generate-background.test.ts
- pnpm exec oxfmt --check --threads=1 src/agents/tools/media-generate-background-shared.ts src/agents/tools/music-generate-background.ts src/agents/tools/music-generate-background.test.ts src/config/schema.help.ts src/config/types.tools.ts docs/automation/tasks.md docs/gateway/config-tools.md CHANGELOG.md
- pnpm config:schema:check
- pnpm config:docs:check
- pnpm check:changelog-attributions
- git diff --check
- OPENCLAW_TESTBOX=1 pnpm check:changed

docs/gateway/config-tools.md

@@ -201,7 +201,7 @@ Configures inbound media understanding (image/audio/video):
     media: {
       concurrency: 2,
       asyncCompletion: {
-        directSend: false, // opt-in: send finished async music/video directly to the channel
+        directSend: false, // opt-in: send finished async video directly to the channel
       },
       audio: {
         enabled: true,
@@ -254,7 +254,7 @@ Configures inbound media understanding (image/audio/video):
 
     **Async completion fields:**
 
-    - `asyncCompletion.directSend`: when `true`, completed async `music_generate` and `video_generate` tasks try direct channel delivery first. Default: `false` (legacy requester-session wake/model-delivery path).
+    - `asyncCompletion.directSend`: when `true`, completed async media tasks that support direct completion delivery try direct channel delivery first. Default: `false` (requester-session wake/model-delivery path). Today this applies to async `video_generate`; async `music_generate` completions stay requester-session mediated even when this is enabled.
 
   </Accordion>
 </AccordionGroup>