feat(terminal): port render state, highlights and the formatter

- render.rs ports render.zig: RenderState, the per-frame snapshot the
  renderer consumes (rows, cells, styles, graphemes, selection,
  highlights, cursor, colors), updated incrementally with Zig's full
  redraw triggers and per-page/per-row dirty tracking. Cells are stored
  struct-of-arrays; use the accessors.
- highlight.rs ports highlight.zig (untracked, tracked, flattened).
- formatter.rs ports formatter.zig: plain, VT and HTML output for
  terminal, screen, page list and page, with selection, rectangle,
  unwrap, trim, palette, codepoint maps, hyperlinks and pin/point maps.
  Screen's test dump helpers now delegate to it.

Cargo.toml also picks up dependencies for the kitty graphics and search
modules that are being ported concurrently.

Test Plan:
- cargo test -p ghostty-terminal --lib (1243 passed; formatter 100/100,
  render 15/15 Zig tests)

crates/ghostty-terminal/src/lib.rs

@@ -1,12 +1,15 @@
 //! Safe page-based terminal memory model.
 #![cfg_attr(test, allow(clippy::unwrap_used))]
 pub mod cursor;
+pub mod formatter;
+pub mod highlight;
 pub mod hyperlink;
 pub mod page;
 pub mod page_list;
 pub mod pin_iter;
 pub mod point;
 pub mod ref_counted_set;
+pub mod render;
 pub mod screen;
 pub mod screen_set;
 pub mod selection;