feat(vt-capi): port the libghostty-vt C API

Ports ZIG/src/lib_vt.zig and terminal/c/* as crates/ghostty-vt-capi
(cdylib + staticlib + rlib, soname libghostty-vt.so) implementing the
unchanged include/ghostty/vt.h + vt/*.h ABI: OSC parser, SGR parser,
key events and key encoding, paste safety, colors, result codes - all
38 native symbols, plus the ghostty_wasm_* helpers on wasm32.

Verification:
- tests/abi.rs generates a C probe from the headers, compiled with cc,
  that checks sizeof/alignof/offsetof of every struct/union, every
  enumerator and #define against Rust, and links every declared symbol;
  nm -D exports equal the declared functions.
- Ghostty's example/c-vt* programs compile unchanged against the Rust
  library (shared and static) and produce the expected output.
- The wasm32 build runs Ghostty's wasm-key-encode/wasm-sgr example
  scripts unmodified under node (upstream's wasm-sgr tag table is stale
  vs sgr.h; a regenerated copy checks full output).

Test Plan:
- cargo test -p ghostty-vt-capi (22 unit + 2 ABI + 5 C + 3 wasm tests)

crates/ghostty-vt-capi/include/ghostty/vt.h

@@ -0,0 +1,87 @@
+/**
+ * @file vt.h
+ *
+ * libghostty-vt - Virtual terminal emulator library
+ * 
+ * This library provides functionality for parsing and handling terminal
+ * escape sequences as well as maintaining terminal state such as styles,
+ * cursor position, screen, scrollback, and more.
+ *
+ * WARNING: This is an incomplete, work-in-progress API. It is not yet
+ * stable and is definitely going to change. 
+ */
+
+/**
+ * @mainpage libghostty-vt - Virtual Terminal Emulator Library
+ *
+ * libghostty-vt is a C library which implements a modern terminal emulator,
+ * extracted from the [Ghostty](https://ghostty.org) terminal emulator.
+ *
+ * libghostty-vt contains the logic for handling the core parts of a terminal
+ * emulator: parsing terminal escape sequences, maintaining terminal state,
+ * encoding input events, etc. It can handle scrollback, line wrapping, 
+ * reflow on resize, and more.
+ *
+ * @warning This library is currently in development and the API is not yet stable.
+ * Breaking changes are expected in future versions. Use with caution in production code.
+ *
+ * @section groups_sec API Reference
+ *
+ * The API is organized into the following groups:
+ * - @ref key "Key Encoding" - Encode key events into terminal sequences
+ * - @ref osc "OSC Parser" - Parse OSC (Operating System Command) sequences
+ * - @ref sgr "SGR Parser" - Parse SGR (Select Graphic Rendition) sequences
+ * - @ref paste "Paste Utilities" - Validate paste data safety
+ * - @ref allocator "Memory Management" - Memory management and custom allocators
+ * - @ref wasm "WebAssembly Utilities" - WebAssembly convenience functions
+ *
+ * @section examples_sec Examples
+ *
+ * Complete working examples:
+ * - @ref c-vt/src/main.c - OSC parser example
+ * - @ref c-vt-key-encode/src/main.c - Key encoding example
+ * - @ref c-vt-paste/src/main.c - Paste safety check example
+ * - @ref c-vt-sgr/src/main.c - SGR parser example
+ *
+ */
+
+/** @example c-vt/src/main.c
+ * This example demonstrates how to use the OSC parser to parse an OSC sequence,
+ * extract command information, and retrieve command-specific data like window titles.
+ */
+
+/** @example c-vt-key-encode/src/main.c
+ * This example demonstrates how to use the key encoder to convert key events
+ * into terminal escape sequences using the Kitty keyboard protocol.
+ */
+
+/** @example c-vt-paste/src/main.c
+ * This example demonstrates how to use the paste utilities to check if
+ * paste data is safe before sending it to the terminal.
+ */
+
+/** @example c-vt-sgr/src/main.c
+ * This example demonstrates how to use the SGR parser to parse terminal
+ * styling sequences and extract text attributes like colors and underline styles.
+ */
+
+#ifndef GHOSTTY_VT_H
+#define GHOSTTY_VT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <ghostty/vt/result.h>
+#include <ghostty/vt/allocator.h>
+#include <ghostty/vt/osc.h>
+#include <ghostty/vt/sgr.h>
+#include <ghostty/vt/key.h>
+#include <ghostty/vt/paste.h>
+#include <ghostty/vt/wasm.h>
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* GHOSTTY_VT_H */