feat(p10-1d): code-c-ast-v1 chunker + snapshot test

Mirrors code-go-ast-v1's chunker pattern. Snapshot test against
tests/fixtures/sample.c (function + typedef struct + typedef enum +
preprocessor) verifies symbol list + lang=c stamping.

Chunks produced (4 total):
- <top-level> glue: includes, defines, static vars, typedefs (lines 1-18)
- parse_record function (lines 20-23)
- print_record function (lines 25-27)
- main function (lines 29-33)

All chunks stamped with lang=c and chunker_version=code-c-ast-v1.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-chunk/tests/fixtures/sample.c

@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define MAX_BUF 4096
+
+typedef enum {
+    OK = 0,
+    ERR_PARSE,
+    ERR_IO,
+} status_t;
+
+typedef struct {
+    int id;
+    char name[64];
+    status_t status;
+} record_t;
+
+static int counter = 0;
+
+int parse_record(const char *line, record_t *out) {
+    if (line == NULL || out == NULL) return ERR_PARSE;
+    return OK;
+}
+
+void print_record(const record_t *r) {
+    printf("[%d] %s (status=%d)\n", r->id, r->name, r->status);
+}
+
+int main(void) {
+    record_t r = { .id = 1, .name = "foo", .status = OK };
+    print_record(&r);
+    return 0;
+}