🐛(frontend) hide tooltips until they have a computed placement

A React Aria overlay is rendered at `top: 0; left: 0` until
`useOverlayPosition` computes its position, and `data-placement` is
only set once that succeeds. When the pointer moves quickly between
triggers, a closing tooltip can mount for its exit animation without
ever being positioned, React Aria does not retry, so it stays
stuck in the top-left corner.

Hide tooltips until they have a `data-placement` set, so unpositioned
tooltips never flash in the corner. Use `visibility` rather than
`display: none`, so the element stays measurable for the positioning
pass.

CHANGELOG.md

@@ -23,6 +23,7 @@ and this project adheres to
 - 🔒️(frontend) upgrade pcre2 to fix CVE-2026-103111
 - 🐛(summary) disable default S3 checksums for GCS-compatible storage
 - 🔒️(summary) redact meeting content from Sentry events
+- 🐛(frontend) hide tooltips until they have a computed placement
 
 ## [1.33.0] - 2026-09-30
 

src/frontend/src/styles/index.css

@@ -103,3 +103,8 @@ html:has(.lk-video-conference) {
   opacity: 1;
   pointer-events: auto;
 }
+
+/* Same workaround as above, see adobe/react-spectrum#10680 */
+[role='tooltip'][data-rac]:not([data-placement]) {
+  visibility: hidden;
+}