example: add c-vt-formatter example

Add an example showing how to use the ghostty-vt terminal and
formatter APIs from C. The example creates a terminal, writes
VT-encoded content with cursor movement and styling sequences,
then formats the screen contents as plain text using the formatter
API.

example/c-vt-formatter/README.md

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+# Example: `ghostty-vt` Terminal Formatter
+
+This contains a simple example of how to use the `ghostty-vt` terminal and
+formatter APIs to create a terminal, write VT-encoded content into it, and
+format the screen contents as plain text.
+
+This uses a `build.zig` and `Zig` to build the C program so that we
+can reuse a lot of our build logic and depend directly on our source
+tree, but Ghostty emits a standard C library that can be used with any
+C tooling.
+
+## Usage
+
+Run the program:
+
+```shell-session
+zig build run
+```

example/c-vt-formatter/build.zig

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+const std = @import("std");
+
+pub fn build(b: *std.Build) void {
+    const target = b.standardTargetOptions(.{});
+    const optimize = b.standardOptimizeOption(.{});
+
+    const run_step = b.step("run", "Run the app");
+
+    const exe_mod = b.createModule(.{
+        .target = target,
+        .optimize = optimize,
+    });
+    exe_mod.addCSourceFiles(.{
+        .root = b.path("src"),
+        .files = &.{"main.c"},
+    });
+
+    // You'll want to use a lazy dependency here so that ghostty is only
+    // downloaded if you actually need it.
+    if (b.lazyDependency("ghostty", .{
+        // Setting simd to false will force a pure static build that
+        // doesn't even require libc, but it has a significant performance
+        // penalty. If your embedding app requires libc anyway, you should
+        // always keep simd enabled.
+        // .simd = false,
+    })) |dep| {
+        exe_mod.linkLibrary(dep.artifact("ghostty-vt"));
+    }
+
+    // Exe
+    const exe = b.addExecutable(.{
+        .name = "c_vt_formatter",
+        .root_module = exe_mod,
+    });
+    b.installArtifact(exe);
+
+    // Run
+    const run_cmd = b.addRunArtifact(exe);
+    run_cmd.step.dependOn(b.getInstallStep());
+    if (b.args) |args| run_cmd.addArgs(args);
+    run_step.dependOn(&run_cmd.step);
+}

example/c-vt-formatter/build.zig.zon

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+.{
+    .name = .c_vt_formatter,
+    .version = "0.0.0",
+    .fingerprint = 0x9e3758265677a0c4,
+    .minimum_zig_version = "0.15.1",
+    .dependencies = .{
+        // Ghostty dependency. In reality, you'd probably use a URL-based
+        // dependency like the one showed (and commented out) below this one.
+        // We use a path dependency here for simplicity and to ensure our
+        // examples always test against the source they're bundled with.
+        .ghostty = .{ .path = "../../" },
+
+        // Example of what a URL-based dependency looks like:
+        // .ghostty = .{
+        //     .url = "https://github.com/ghostty-org/ghostty/archive/COMMIT.tar.gz",
+        //     .hash = "N-V-__8AAMVLTABmYkLqhZPLXnMl-KyN38R8UVYqGrxqO36s",
+        // },
+    },
+    .paths = .{
+        "build.zig",
+        "build.zig.zon",
+        "src",
+    },
+}

example/c-vt-formatter/src/main.c

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+#include <assert.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <ghostty/vt.h>
+
+int main() {
+  // Create a terminal with a small grid
+  GhosttyTerminal terminal;
+  GhosttyTerminalOptions opts = {
+    .cols = 80,
+    .rows = 24,
+    .max_scrollback = 0,
+  };
+  GhosttyResult result = ghostty_terminal_new(NULL, &terminal, opts);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Write VT-encoded content into the terminal to exercise various
+  // cursor movement and styling sequences.
+  const char *commands[] = {
+    "Line 1: Hello World!\r\n",           // Simple text on row 1
+    "Line 2: \033[1mBold\033[0m and "     // Bold text on row 2
+      "\033[4mUnderline\033[0m\r\n",
+    "Line 3: placeholder\r\n",            // Will be overwritten below
+    "\033[3;1H",                          // CUP: move cursor back to row 3, col 1
+    "\033[2K",                            // EL:  erase the entire line
+    "Line 3: Overwritten!\r\n",           // Rewrite row 3 with new content
+    "\033[5;10H",                         // CUP: jump to row 5, col 10
+    "Placed at (5,10)",                   // Write at that position
+    "\033[1;72H",                         // CUP: jump to row 1, col 72
+    "RIGHT->",                            // Near the right edge of row 1
+  };
+  for (size_t i = 0; i < sizeof(commands) / sizeof(commands[0]); i++) {
+    ghostty_terminal_vt_write(terminal, (const uint8_t *)commands[i],
+                              strlen(commands[i]));
+  }
+
+  // Create a plain-text formatter for the terminal
+  GhosttyFormatterTerminalOptions fmt_opts = GHOSTTY_INIT_SIZED(GhosttyFormatterTerminalOptions);
+  fmt_opts.emit = GHOSTTY_FORMATTER_FORMAT_PLAIN;
+  fmt_opts.trim = true;
+
+  GhosttyFormatter formatter;
+  result = ghostty_formatter_terminal_new(NULL, &formatter, terminal, fmt_opts);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Format into an allocated buffer
+  uint8_t *buf = NULL;
+  size_t len = 0;
+  result = ghostty_formatter_format_alloc(formatter, NULL, &buf, &len);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Print the formatted output
+  printf("Formatted output (%zu bytes):\n", len);
+  fwrite(buf, 1, len, stdout);
+  printf("\n");
+
+  // Clean up
+  free(buf);
+  ghostty_formatter_free(formatter);
+  ghostty_terminal_free(terminal);
+  return 0;
+}