bazel.build Migration: Investigate performance issues

- "Typing in the AI text box at the bottom of the screen is very laggy. I also think since there is one top center we shouldn't have one taking up space at the bottom as well" (https://github.com/bazelbuild/bazel/issues/30598#issuecomment-5221011907)
- "Performance is really bad on Safari, the page takes several seconds before it's scrollable." (https://github.com/bazelbuild/bazel/issues/30598#issuecomment-5221326039)

Start with the bazel.build migration work and the two performance reports linked from issue #30598. Reproduce the lag while typing in the AI text box and the delayed scrolling on Safari, then trace the relevant page behavior. Done means identifying the causes and documenting actionable findings.

Written by the indexing model from the issue text.