feat: papis / Zotero integration — export search results to reference manager #18

Summary

Allow mosaic search results to be exported directly into Papis or Zotero reference management libraries.

Motivation

Many researchers manage their bibliography with Papis or Zotero. Exporting MOSAIC results directly into these tools would remove the manual copy-paste step and keep metadata in sync with the local cache.

Proposed behaviour

# Add all results to the default Papis library
mosaic search "attention is all you need" --oa-only | mosaic export --papis

# Add to a specific Papis library
mosaic search "diffusion models" --export papis --papis-lib mylib

# Add to Zotero (requires Zotero local API running on port 23119)
mosaic search "protein folding" --export zotero --zotero-collection "AI Biology"

# Export from a previous search (cache)
mosaic export --papis --query "diffusion models"

Implementation notes

Papis:

• Invoke papis add --from-doi <doi> for each result (if DOI known)
• Or write a temporary BibTeX file and papis add --from-bibtex
• Optionally copy the downloaded PDF to the Papis document folder

Zotero:

• Use the Zotero local API (port 23119) — no credentials needed
• POST /users/0/items with CSL-JSON payload built from Paper fields
• Attach PDF if already downloaded

Dependency: Papis integration requires papis to be installed separately. Zotero integration has no Python dependency (pure HTTP to localhost).

Priority

Tier 2 — moderate value, moderate complexity