feat: follow any open issue from search (Closes #1303)

tests/e2e/test_mobile_search_preview_navigation.py

@@ -32,7 +32,16 @@ def test_rendered_mobile_search_preview_navigation_preserves_reading_space_and_d
         page.locator("#search-preview-conversation").evaluate("node => node.style.minHeight = '500px'")
         page.locator("#search-preview-reply-workspace").evaluate("node => node.style.minHeight = '500px'")
         page.locator("#search-preview-actions").evaluate("node => node.style.minHeight = '300px'")
-        page.locator("#watch-search-result").evaluate("node => { node.hidden = false; node.textContent = 'Watch issue'; }")
+        page.add_script_tag(path=FRONTEND / "search-preview.js")
+        page.evaluate("""() => {
+          const assignedIssue = {
+            kind:'issue', state:'open', claimable:false, assigned_to_me:false,
+            assignees:['alexander'], watching:false,
+          };
+          globalThis.renderSearchPreviewWatch(
+            assignedIssue, {status:'ready'}, document.querySelector('#watch-search-result')
+          );
+        }""")
         page.add_script_tag(path=FRONTEND / "mobile-search-preview-nav.js")
 
         watch = page.locator("#watch-search-result")