Fix build error with libgit2 -Wmissing-field-initializers

Build fails at pass_githistory.c:171 with:

  error: missing field 'interhunk_lines' initializer
         [-Werror,-Wmissing-field-initializers]
    git_diff_options diff_opts = GIT_DIFF_OPTIONS_INIT;

codebase-memory-mcp at 75b5dcb has this issue. The GIT_DIFF_OPTIONS_INIT
macro does not list all struct fields, which clang flags as an error
under -Werror.

Replace the macro with the runtime git_diff_options_init() API, which
properly initializes all fields. Available since libgit2 0.28.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jsyrjala

src/pipeline/pass_githistory.c

@@ -168,7 +168,8 @@ static int parse_git_log(const char *repo_path, commit_t **out, int *out_count)
 
         /* Diff parent_tree → tree to find changed files */
         git_diff *diff = NULL;
-        git_diff_options diff_opts = GIT_DIFF_OPTIONS_INIT;
+        git_diff_options diff_opts;
+        git_diff_options_init(&diff_opts, GIT_DIFF_OPTIONS_VERSION);
         if (git_diff_tree_to_tree(&diff, repo, parent_tree, tree, &diff_opts) == 0) {
             commit_t current = {0};