fix: TOC anchor navigation - remove anchor text from parsed content

- Fix parse_blocks: after extracting anchor from \\x03..\\x04 markers,
  remove the anchor text too (was contaminating display text)
- When TOC jump occurs, clear pending_anchor to prevent saved position
  from overriding the TOC navigation on first frame
- Add tests for heading with/without anchor parsing

src/app.rs

@@ -382,6 +382,7 @@ BgType::Custom(ref path) if !path.is_empty() => {
             if let Some(section) = action.jump_to_section {
                 self.state.current_section = section;
                 self.state.current_page = 0;
+                self.state.pending_anchor = None;
                 if let Some(ref anchor) = action.jump_to_anchor {
                     if let Some(ref book) = self.state.book {
                         if section < book.sections.len() {