Migrate all boolean-typed parameters, return values, struct fields, and local variables from `int` (with 0/1 convention) to C99 `bool` (`true`/`false`). Update corresponding comments, macro definitions, and documentation strings to use `true`/`false` terminology instead of "non-zero"/"zero". Add `#include <stdbool.h>` to `src/main.c`, `src/wren_compiler.c`, and `src/wren_value.h`. Remove the stale TODO comment in `src/wren_common.h` that originally proposed this change.