Fix non-exhaustive Inline match in loki-pdf text writer

Add FootnoteRef arm (empty string — PDF footnotes not yet implemented)
to the two collect_text/space_width map sites in para.rs and renderer.rs.

https://claude.ai/code/session_01MokDdUw2YPFTgD3ZsZ7Scn

Author: claude

src-tauri/formats/pdf/src/writer/text/para.rs

@@ -200,6 +200,7 @@ fn collect_text(content: &[Inline]) -> String {
         .map(|i| match i {
             Inline::Text { text, .. } => text.as_str(),
             Inline::LineBreak => "\n",
+            Inline::FootnoteRef { .. } => "",
         })
         .collect()
 }

src-tauri/formats/pdf/src/writer/text/renderer.rs

@@ -137,6 +137,7 @@ fn is_finished(
                     .map(|i| match i {
                         Inline::Text { text, .. } => text.as_str(),
                         Inline::LineBreak => "\n",
+                        Inline::FootnoteRef { .. } => "",
                     })
                     .collect();
                 let font_size = props.font_size;