fix(web): de-reactify open-transition trackers in 3 more modals/banners (#687)

Sweep follow-up to BUG-1687. ConnectBanner, CreateCollectionModal, and
ConnectWorkspaceModal each tracked their open→close transition with a
`$state` variable (`prevOpen`/`lastOpen`) that their `$effect`/`$effect.pre`
both read and wrote — the same self-invalidating pattern that silently
wedges Svelte's effect scheduler in production builds on close.

Make each tracker a plain `let` (they're only used for edge-detection inside
the effect), so the effects depend solely on `open`/`connectOpen` and never
re-trigger themselves. Found via a codebase-wide audit; these were the only
other genuine matches.

web/src/lib/components/ConnectBanner.svelte

@@ -97,8 +97,11 @@
 	// doesn't know which tab actually triggered the agent connection;
 	// any close is good-enough signal. Tracking `prevOpen` is the
 	// minimum reactive shape to detect the open → closed transition
-	// without re-firing on every render.
-	let prevOpen = $state(false);
+	// without re-firing on every render. PLAIN variable (not $state): it's
+	// only read/written for edge-detection inside the effect below — making
+	// it $state makes the effect self-invalidating, which silently wedges
+	// the effect scheduler in prod builds (see BUG-1687 / ShareDialog).
+	let prevOpen = false;
 	$effect.pre(() => {
 		if (prevOpen && !connectOpen) {
 			refreshHasAgentActivity(wsSlug);

web/src/lib/components/ConnectWorkspaceModal.svelte

@@ -57,7 +57,10 @@
 	// user manually switched tabs, so we use a $state seeded by an $effect
 	// that fires only on the open→true transition.
 	let activeTab = $state<PrimaryTab>('cli');
-	let lastOpen = $state(false);
+	// PLAIN variable (not $state): only used for edge-detection inside the
+	// effect below. As $state it makes the effect self-invalidating, which
+	// silently wedges the effect scheduler in prod builds (BUG-1687).
+	let lastOpen = false;
 	$effect(() => {
 		if (open && !lastOpen) {
 			activeTab = mcpPublicUrl ? 'agent' : 'cli';

web/src/lib/components/collections/CreateCollectionModal.svelte

@@ -108,8 +108,11 @@
 		}
 	});
 
-	// Track previous open state to detect open transitions
-	let prevOpen = $state(false);
+	// Track previous open state to detect open transitions. PLAIN variable
+	// (not $state): only used for edge-detection inside the effect below.
+	// As $state it makes the effect self-invalidating, silently wedging the
+	// effect scheduler in prod builds (see BUG-1687 / ShareDialog).
+	let prevOpen = false;
 
 	// Reset to step 1 whenever the modal opens (false -> true transition)
 	$effect.pre(() => {