Replace the physical ekp-region renderer with ekp-buffer text-property projection backed by shared semantic layout plans and stable live-edit transactions.
Optimize the C-backed resize hot path, and add deterministic performance, ERT, GUI, fuzz, release, and documentation coverage for task017 through task032.
BREAKING CHANGE: require ekp-buffer instead of ekp-region and rename module-owned ekp-region-* settings to ekp-buffer-*.
