fix: remove rel=noopener from all session/instance links to enable tab reuse

rel=noopener forces a fresh browsing context, breaking target name matching
and window reference tracking across browsers.

Changes:
- use-instance-actions.ts: track opened tabs in Map, call .focus() on existing
- session-card.tsx: all Open buttons now go through handleOpen callback
- app-shell.tsx: sidebar session links use target='session-{id}' + noreferrer
- workspace-instance-chips.tsx: remove noopener from chip links
- instance-list.tsx: remove noopener from Open links
- WorkspaceDetailPage.tsx: use named target + noreferrer

Quality gates: tsc --noEmit pass, npm run build pass, 80/80 tests pass

apps/web/src/hooks/use-instance-actions.ts

@@ -1,4 +1,4 @@
-import { useState, useCallback } from "react";
+import { useState, useCallback, useRef } from "react";
 import {
 	stopInstance,
 	deleteInstance,
@@ -33,18 +33,27 @@ export function useInstanceActions(
 		null,
 	);
 	const [dirtyDeleteFiles, setDirtyDeleteFiles] = useState<string[]>([]);
+	const tabRefs = useRef<Map<string, Window | null>>(new Map());
 
 	const handleOpen = useCallback((session: Session) => {
-		const tabName = `session-${session.id}`;
+		const key = session.id;
+		const existing = tabRefs.current.get(key);
+		if (existing && !existing.closed) {
+			existing.focus();
+			return;
+		}
+
+		let url: string;
 		if (session.url) {
-			window.open(session.url, tabName);
-			return;
+			url = session.url;
+		} else if (session.tool_type_interfaces?.includes("terminal")) {
+			url = `/instances/${session.id}/terminal`;
+		} else {
+			url = `/projects/${session.project_id}`;
 		}
-		if (session.tool_type_interfaces?.includes("terminal")) {
-			window.open(`/instances/${session.id}/terminal`, tabName);
-			return;
-		}
-		window.open(`/projects/${session.project_id}`, tabName);
+
+		const w = window.open(url, `session-${session.id}`);
+		tabRefs.current.set(key, w);
 	}, []);
 
 	const handleStart = useCallback(