fix(tui): "Model not found: system/notification" error displayed for synthetic notifyPM messages

[randomm]

Bug

When notifyPM fires, the TUI shows error: Model not found: system/notification

Cause

pulse-verdicts.ts notifyPM() creates synthetic messages with modelID: "notification" and providerID: "system". These are never sent to an LLM — they're direct store writes. But the TUI message renderer tries to look up the model system/notification and fails when it can't find it.

Impact

Visual only — the notification IS delivered correctly (PM session receives the message). But the red error is confusing.

Fix

The TUI renderer should handle synthetic/unknown model IDs gracefully — either show a generic icon/label, or notifyPM should use a model ID that the TUI already knows how to render (e.g. use the PM session's actual model ID).

Acceptance Criteria

• No "Model not found" error shown for notifyPM messages
• Notification messages render cleanly in TUI