feat(config): P3 config batch — group 6 (RSS fidelity + rss_name/rss_max_items)

write_rss now emits upstream's full RSS 2.0 structure:
- xmlns:atom on <rss>; channel <link> points at the diary index page
  (base_url + diary_rel + diary_index + .html), not bare base_url.
- <atom:link rel="self"> to base_url + rss_name.
- channel + per-item <pubDate> (RFC-822, derived from the diary date;
  1970-01-01=Thu weekday math via to_days_epoch).
- per-item <guid isPermaLink="false"> holding the bare date.
- per-item <![CDATA[ rendered page body ]]> (render_entry_body reads+parses
  the entry and renders body-only with the wiki's colour/valid-tag/emoji opts;
  cdata_safe splits any literal ]]>).
- rss_name drives the output filename; rss_max_items caps the feed (0 =
  unlimited).

Tests: updated write_rss_uses_base_url_for_public_links for the new channel
link/guid/atom/pubDate; new write_rss_honours_rss_name_and_max_items. Full
rust suite + clippy clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/nuwiki-lsp/tests/html_export.rs

@@ -613,13 +613,48 @@ fn write_rss_uses_base_url_for_public_links() {
     }];
     let path = nuwiki_lsp::commands::export_ops::write_rss(&c, &entries).unwrap();
     let xml = std::fs::read_to_string(&path).unwrap();
-    // Channel + item links use the public base URL, not file://.
-    assert!(xml.contains("<link>https://example.com/wiki/</link>"));
+    // Channel link points at the diary index page (upstream fidelity); item
+    // link is the public per-entry URL.
+    assert!(
+        xml.contains("<link>https://example.com/wiki/diary/diary.html</link>"),
+        "channel link: {xml}"
+    );
     assert!(xml.contains("<link>https://example.com/wiki/diary/2026-05-11.html</link>"));
-    assert!(xml.contains("<guid>https://example.com/wiki/diary/2026-05-11.html</guid>"));
+    // guid is the bare date, isPermaLink=false.
+    assert!(
+        xml.contains("<guid isPermaLink=\"false\">2026-05-11</guid>"),
+        "guid: {xml}"
+    );
+    // atom:link self + a pubDate are present.
+    assert!(xml.contains("rel=\"self\""), "atom:link: {xml}");
+    assert!(xml.contains("<pubDate>"), "pubDate: {xml}");
     assert!(!xml.contains("file:///tmp/diary"));
 }
 
+#[test]
+fn write_rss_honours_rss_name_and_max_items() {
+    use nuwiki_lsp::diary::DiaryEntry;
+    use tower_lsp::lsp_types::Url;
+    let root = temp_root("rss_cap");
+    let mut c = WikiConfig::from_root(root.clone());
+    c.html = HtmlConfig::from_root(&root);
+    c.html.rss_name = "feed.xml".into();
+    c.html.rss_max_items = 2;
+    let entries: Vec<DiaryEntry> = (1..=5)
+        .map(|d| DiaryEntry {
+            date: DiaryDate::from_ymd(2026, 5, d).unwrap(),
+            uri: Url::parse(&format!("file:///tmp/diary/2026-05-0{d}.wiki")).unwrap(),
+        })
+        .collect();
+    let path = nuwiki_lsp::commands::export_ops::write_rss(&c, &entries).unwrap();
+    assert!(path.ends_with("feed.xml"), "rss_name: {path:?}");
+    let xml = std::fs::read_to_string(&path).unwrap();
+    // Capped at 2 items (newest first: 05-05, 05-04).
+    assert_eq!(xml.matches("<item>").count(), 2, "cap: {xml}");
+    assert!(xml.contains("2026-05-05") && xml.contains("2026-05-04"));
+    assert!(!xml.contains("2026-05-03"), "older items dropped: {xml}");
+}
+
 #[test]
 fn write_page_invokes_custom_wiki2html_converter() {
     let root = temp_root("custom_w2h");