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)

Cargo.lock

@@ -562,6 +562,15 @@ version = "1.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "790eea4361631c5e7d22598ecd5723ff611904e3344ce8720784c93e3d83d40b"
 
+[[package]]
+name = "crossbeam-channel"
+version = "0.5.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98b0cc327b5bc766e7fda9c9260cc0fa81b43a8e240440422dff70788e3f9ef1"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-utils"
 version = "0.8.23"
@@ -1351,19 +1360,31 @@ dependencies = [
 name = "ghostty-terminal"
 version = "0.1.0"
 dependencies = [
+ "crossbeam-channel",
+ "flate2",
  "ghostty-config",
  "ghostty-datastruct",
  "ghostty-unicode",
  "ghostty-vt",
  "log",
  "onig",
+ "png",
+ "rustix",
+ "thiserror 2.0.21",
 ]
 
 [[package]]
 name = "ghostty-termio"
 version = "0.1.0"
 dependencies = [
+ "crossbeam-channel",
+ "ghostty-apprt",
+ "ghostty-config",
+ "ghostty-datastruct",
  "ghostty-os",
+ "ghostty-renderer",
+ "ghostty-terminal",
+ "ghostty-vt",
  "libc",
  "log",
  "nix 0.31.3",