feat(web): NL-canonical onboarding banner copy (TASK-1851) (#743)

OnboardingNudgeBanner hardcoded `/pad onboard`, which contradicted the
NL-canonical messaging shipped in TASK-1849 (and is wrong for non-Claude-Code
agents). Lead with natural language ("say set up my workspace") instead — the
universal trigger that works regardless of which agent the user connects.

ConnectBanner audited — no slug reference, left as-is. Per-surface shortcut
rendering belongs in the connect modal's surface-aware kickoff (TASK-1852),
where the chosen tool is known.

Parent: PLAN-1847 (Phase 2, task A).

Claude-Session: https://claude.ai/code/session_01KmxkPxLksjf1pmrZDpsnTJ

web/src/lib/components/OnboardingNudgeBanner.svelte

@@ -58,8 +58,8 @@
 	<div class="nudge-body">
 		<span class="nudge-title">Set up your workspace</span>
 		<p class="nudge-text">
-			Your workspace is ready. Connect your agent and type
-			<code>/pad onboard</code> to walk through setting it up.
+			Your workspace is ready. Connect your agent, then just say
+			<code>set up my workspace</code> &mdash; it'll walk you through setup.
 		</p>
 	</div>
 	<span class="nudge-actions">