Add dynamic type field to BibTeX template

- Use @{{doc[type]}} to dynamically set BibTeX entry type
- Add back booktitle field for conference papers
- Properly escape braces using double braces for literal output

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

modules/papis.nix

@@ -48,11 +48,12 @@
 
   # Papis BibTeX template
   home.file."Library/Application Support/papis/templates/bibtex.template".text = ''
-    @article{{{doc[ref]},
+    @{{doc[type]}}{{{doc[ref]},
       author = {{{doc[author]}}},
       title = {{{doc[title]}}},
       year = {{{doc[year]}}},
       journal = {{{doc[journal]}}},
+      booktitle = {{{doc[booktitle]}}},
       volume = {{{doc[volume]}}},
       number = {{{doc[number]}}},
       pages = {{{doc[pages]}}},