Show input-method composition in the browser's own text fields (#1)

The URL bar, bookmarks search, vi command line and dialog fields show an input method's composition at the caret and report their caret; cce-ui pinned to e8298ae.

 CLAUDE.md   |  31 +++++
 Cargo.toml  |   2 +-
 src/main.rs | 399 +++++++++++++++++++++++++++++++++++++-----------------------
 3 files changed, 278 insertions(+), 154 deletions(-)