fix(ghostty): report terminal size when mode 2048 is enabled

Adds in-band resize notifications for Ghostty-backed terminals using DEC mode 2048.

The core reports the current grid size when the mode is enabled or restored, and whenever the dimensions change while it is active. WTerm.resize() delivers these reports through onData immediately, including during synchronized output. Pixel dimensions are reported as zero because the core only tracks character dimensions.

Previously, the wrapper advertised support for mode 2048 but never sent size reports. This caused Neovim to stop handling SIGWINCH and retain its old grid after a resize.