Offer effects wherever they run, and say what they cost

- Drops the desktop test. Measured, it sorted devices by the wrong thing:
  a phone on the fast path held 99% of its frame rate and was refused, a
  desktop on the slow one held 73% and was allowed.
- What the cost tracks is the processing path, and Safari and Firefox take
  the slow one on every platform. That is told, not enforced: the cost is
  smoothness, the reason to pay it is privacy, and only the user knows
  whether they would rather show the room they are sitting in.
- The first effect of a session takes a while to prepare, so its own tile
  spins where its tick will go, until a frame has actually come out of the
  pipeline. The promises say nothing useful about when that is: attaching
  resolves in about three seconds and switching in none at all, and the
  slow path then holds the page still for twelve to fifteen more. The
  spinner turns by rotating, which a browser composites, so it keeps moving
  through a pause that has stopped everything else.
- Copy is the exploration's and needs an owner (S3).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

locales/en/app.json

@@ -27,6 +27,9 @@
     "upload_file": "Upload file"
   },
   "analytics_notice": "By participating in this beta, you consent to the collection of anonymous data, which we use to improve the product. You can find more information about which data we track in our <2>Privacy Policy</2> and our <6>Cookie Policy</6>.",
+  "background_effects": {
+    "slow_in_this_browser": "This browser runs background effects slowly, so other people may see your video stutter."
+  },
   "call_ended_view": {
     "create_account_button": "Create account",
     "create_account_prompt": "<0>Why not finish by setting up a password to keep your account?</0><1>You'll be able to keep your name and set an avatar for use on future calls</1>",