feat: enforce output version v1 and add version subcommand

tests/render_markdown_tests.rs

@@ -7,12 +7,13 @@ use gitea_pr_review::render::markdown::render_markdown;
 #[test]
 fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
     let doc = PrReviewDocument {
+        version: "v1".into(),
         meta: PrMeta {
             repo: "org/repo".into(),
             pr_index: 7,
             title: "Fix parser".into(),
             description: Some("PR body".into()),
-            fetched_at: Some("2026-04-08T12:34:56Z".into()),
+            fetched_at: "2026-04-08T12:34:56Z".into(),
             state: "open".into(),
             author: "alice".into(),
             base_branch: "main".into(),
@@ -73,6 +74,7 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
 
     assert!(md.contains("# org/repo `#7` Fix parser"));
     assert!(md.contains("## Metadata"));
+    assert!(md.contains("> version: v1"));
     assert!(md.contains("> fetched at: 2026-04-08T12:34:56Z"));
     assert!(md.contains("## Commits"));
     assert!(md.contains("## Diff Stat"));
@@ -96,12 +98,13 @@ fn render_markdown_includes_expected_sections_and_preserves_comment_markdown() {
 fn render_markdown_uses_minimal_fence_for_plain_text() {
     let body = "plain text";
     let doc = PrReviewDocument {
+        version: "v1".into(),
         meta: PrMeta {
             repo: "org/repo".into(),
             pr_index: 1,
             title: "T".into(),
             description: None,
-            fetched_at: None,
+            fetched_at: "2026-04-08T12:34:56Z".into(),
             state: "open".into(),
             author: "alice".into(),
             base_branch: "main".into(),