refactor(wake): drop the redundant per-wake Subscription id from the wake digest

Summary

MX-loop cleanup (the agents get the wake noise, so this is ours to drive). The wake digest ends every delivery with \n\nSubscription: ${subId} (ai/daemons/wake/daemon.mjs buildWakeDigest). It is redundant noise for the consuming agent:

• Never consumed in the wake-handling flow. Acting on a wake, the agent uses the message/task IDs (list_messages/get_message) — never the subscription id.
• Stable per agent. One WAKE_SUBSCRIPTION per agent → the same id on every wake, so per-wake it carries zero new information — pure repeated token-cost (the same cost #13137 trimmed from the directive).
• Its one consumer is out-of-band. Only manage_wake_subscription (unsubscribe/update/resync) needs a subscriptionId, and action: list returns it on demand. Nothing in the normal flow needs it inline.

Refs #13137 (wake token-cost family).

Acceptance Criteria

• buildWakeDigest no longer appends the Subscription: ${subId} line; the subId param is removed (it was used only there) + both call sites + the JSDoc updated.
• The lane-directive append (heartbeat-only, #13141) still composes cleanly after the change.
• daemon.spec asserts the delivered digest does NOT contain Subscription: (mirrors the existing not.toContain('\nWindow:') lock).

Out of scope

The rest of the digest (priority header, event breakdown, recipient identity) — all carry per-wake signal; only the stable subscription id is dropped.

Origin Session ID: 4cc428e3-cf36-4324-8646-1b96cb23fa4a