feat(which-key): add passive rendering widget crate with multi-column grid layout
Decoupled from evil-keys — accepts generic KeyHint data from any source.
Ports which-key.nvim's dimension calculation and column-major grid algorithm.
Features: unicode-aware truncation, multi-level sorting (group/alphanum/natural/case),
configurable styling via builder pattern, auto-sizing with Position-based placement.
76 tests covering dim() (31 ported from nvim), grid layout, truncation, padding, and sorting.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/claude-agent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
Alexander
498e92f2e4