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/examples/c/c-vt-sgr.c

@@ -0,0 +1,131 @@
+#include <assert.h>
+#include <stdio.h>
+#include <ghostty/vt.h>
+
+int main() {
+  // Create parser
+  GhosttySgrParser parser;
+  GhosttyResult result = ghostty_sgr_new(NULL, &parser);
+  assert(result == GHOSTTY_SUCCESS);
+
+  // Parse a complex SGR sequence from Kakoune
+  // This corresponds to the escape sequence:
+  // ESC[4:3;38;2;51;51;51;48;2;170;170;170;58;2;255;97;136m
+  //
+  // Breaking down the sequence:
+  // - 4:3 = curly underline (colon-separated sub-parameters)
+  // - 38;2;51;51;51 = foreground RGB color (51, 51, 51) - dark gray
+  // - 48;2;170;170;170 = background RGB color (170, 170, 170) - light gray
+  // - 58;2;255;97;136 = underline RGB color (255, 97, 136) - pink
+  uint16_t params[] = {4, 3, 38, 2, 51, 51, 51, 48, 2, 170, 170, 170, 58, 2, 255, 97, 136};
+  
+  // Separator array: ':' at position 0 (between 4 and 3), ';' elsewhere
+  char separators[] = ";;;;;;;;;;;;;;;;";
+  separators[0] = ':';
+  
+  result = ghostty_sgr_set_params(parser, params, separators, sizeof(params) / sizeof(params[0]));
+  assert(result == GHOSTTY_SUCCESS);
+
+  printf("Parsing Kakoune SGR sequence:\n");
+  printf("ESC[4:3;38;2;51;51;51;48;2;170;170;170;58;2;255;97;136m\n\n");
+
+  // Iterate through attributes
+  GhosttySgrAttribute attr;
+  int count = 0;
+  while (ghostty_sgr_next(parser, &attr)) {
+    count++;
+    printf("Attribute %d: ", count);
+    
+    switch (attr.tag) {
+      case GHOSTTY_SGR_ATTR_UNDERLINE:
+        printf("Underline style = ");
+        switch (attr.value.underline) {
+          case GHOSTTY_SGR_UNDERLINE_NONE:
+            printf("none\n");
+            break;
+          case GHOSTTY_SGR_UNDERLINE_SINGLE:
+            printf("single\n");
+            break;
+          case GHOSTTY_SGR_UNDERLINE_DOUBLE:
+            printf("double\n");
+            break;
+          case GHOSTTY_SGR_UNDERLINE_CURLY:
+            printf("curly\n");
+            break;
+          case GHOSTTY_SGR_UNDERLINE_DOTTED:
+            printf("dotted\n");
+            break;
+          case GHOSTTY_SGR_UNDERLINE_DASHED:
+            printf("dashed\n");
+            break;
+          default:
+            printf("unknown (%d)\n", attr.value.underline);
+            break;
+        }
+        break;
+
+      case GHOSTTY_SGR_ATTR_DIRECT_COLOR_FG:
+        printf("Foreground RGB = (%d, %d, %d)\n",
+               attr.value.direct_color_fg.r,
+               attr.value.direct_color_fg.g,
+               attr.value.direct_color_fg.b);
+        break;
+
+      case GHOSTTY_SGR_ATTR_DIRECT_COLOR_BG:
+        printf("Background RGB = (%d, %d, %d)\n",
+               attr.value.direct_color_bg.r,
+               attr.value.direct_color_bg.g,
+               attr.value.direct_color_bg.b);
+        break;
+
+      case GHOSTTY_SGR_ATTR_UNDERLINE_COLOR:
+        printf("Underline color RGB = (%d, %d, %d)\n",
+               attr.value.underline_color.r,
+               attr.value.underline_color.g,
+               attr.value.underline_color.b);
+        break;
+
+      case GHOSTTY_SGR_ATTR_FG_8:
+        printf("Foreground 8-color = %d\n", attr.value.fg_8);
+        break;
+
+      case GHOSTTY_SGR_ATTR_BG_8:
+        printf("Background 8-color = %d\n", attr.value.bg_8);
+        break;
+
+      case GHOSTTY_SGR_ATTR_FG_256:
+        printf("Foreground 256-color = %d\n", attr.value.fg_256);
+        break;
+
+      case GHOSTTY_SGR_ATTR_BG_256:
+        printf("Background 256-color = %d\n", attr.value.bg_256);
+        break;
+
+      case GHOSTTY_SGR_ATTR_BOLD:
+        printf("Bold\n");
+        break;
+
+      case GHOSTTY_SGR_ATTR_ITALIC:
+        printf("Italic\n");
+        break;
+
+      case GHOSTTY_SGR_ATTR_UNSET:
+        printf("Reset all attributes\n");
+        break;
+
+      case GHOSTTY_SGR_ATTR_UNKNOWN:
+        printf("Unknown attribute\n");
+        break;
+
+      default:
+        printf("Other attribute (tag=%d)\n", attr.tag);
+        break;
+    }
+  }
+
+  printf("\nTotal attributes parsed: %d\n", count);
+
+  // Cleanup
+  ghostty_sgr_free(parser);
+  return 0;
+}