feat: scipdf plugin + PDF coverage tracker for skin-subs retrieval (refs #257)

Installed zotero-scipdf v8.0.4 (syt2/zotero-scipdf) in Zotero 8 container:
- 7 SciHub mirrors registered as Zotero PDF resolvers
- Works with Zotero's native "Find Available PDF" feature
- Also installed alongside ZotMoov (existing)

PDF coverage script: dev/scripts/check_pdf_coverage.py
- Reports DOI count, PDF attachment count, coverage by item type
- Current baseline: 9,658 DOIs (94%), 0 PDFs retrieved

To retrieve: open Zotero GUI, select Skin Substitutes collection,
Ctrl+A, right-click → Find Available PDF. Plugin handles Unpaywall
first, then SciHub mirrors sequentially.

dev/scripts/check_pdf_coverage.py

@@ -0,0 +1,92 @@
+"""Check PDF retrieval coverage for skin substitute evidence base.
+
+Reports how many Zotero items have PDF attachments vs DOI-bearing items
+that could potentially be retrieved. Run after using Zotero's
+"Find Available PDF" with the scipdf plugin.
+
+Usage:
+    uv run python dev/scripts/check_pdf_coverage.py
+"""
+
+from __future__ import annotations
+
+import sqlite3
+from pathlib import Path
+
+from conf import path as conf_path
+
+ZOTERO_DB = str(conf_path("db.zotero"))
+
+
+def main() -> None:
+    print("Checking PDF coverage for skin-subs items in Zotero ...\n")
+
+    con = sqlite3.connect(ZOTERO_DB, timeout=10)
+    con.row_factory = sqlite3.Row
+
+    # Total skin-subs items
+    total = con.execute("""
+        SELECT count(DISTINCT it.itemID) FROM itemTags it
+        JOIN tags t ON it.tagID = t.tagID
+        WHERE t.name = 'module:skin-subs'
+    """).fetchone()[0]
+
+    # Items with DOI (retrievable)
+    with_doi = con.execute("""
+        SELECT count(DISTINCT i.itemID) FROM items i
+        JOIN itemTags it ON i.itemID = it.itemID
+        JOIN tags t ON it.tagID = t.tagID
+        JOIN itemData id ON i.itemID = id.itemID
+        WHERE t.name = 'module:skin-subs' AND id.fieldID = 8
+    """).fetchone()[0]
+
+    # Items with PDF attachments
+    with_pdf = con.execute("""
+        SELECT count(DISTINCT parent.itemID) FROM items parent
+        JOIN itemTags it ON parent.itemID = it.itemID
+        JOIN tags t ON it.tagID = t.tagID
+        JOIN itemAttachments ia ON ia.parentItemID = parent.itemID
+        JOIN items att ON ia.itemID = att.itemID
+        WHERE t.name = 'module:skin-subs'
+          AND ia.contentType = 'application/pdf'
+    """).fetchone()[0]
+
+    print(f"Total skin-subs items:     {total:>6}")
+    print(f"Items with DOI:            {with_doi:>6} ({with_doi * 100 // total}%)")
+    print(f"Items with PDF attached:   {with_pdf:>6} ({with_pdf * 100 // max(total, 1)}%)")
+    print(f"DOIs without PDF:          {with_doi - with_pdf:>6}")
+    print(f"Coverage (of DOI items):   {with_pdf * 100 // max(with_doi, 1)}%")
+
+    # Breakdown by item type
+    print("\nBy item type:")
+    for r in con.execute("""
+        SELECT it2.typeName,
+               count(DISTINCT i.itemID) as total,
+               count(DISTINCT CASE WHEN ia.itemID IS NOT NULL THEN i.itemID END) as with_pdf
+        FROM items i
+        JOIN itemTags it ON i.itemID = it.itemID
+        JOIN tags t ON it.tagID = t.tagID
+        JOIN itemTypes it2 ON i.itemTypeID = it2.itemTypeID
+        LEFT JOIN itemAttachments ia ON ia.parentItemID = i.itemID
+            AND ia.contentType = 'application/pdf'
+        WHERE t.name = 'module:skin-subs'
+        GROUP BY it2.typeName
+        ORDER BY total DESC
+    """).fetchall():
+        pct = r["with_pdf"] * 100 // max(r["total"], 1)
+        print(f"  {r['typeName']:20s}  total={r['total']:>5}  pdf={r['with_pdf']:>5}  ({pct}%)")
+
+    # Storage size
+    storage = Path(conf_path("storage.zotero"))
+    if storage.exists():
+        total_bytes = sum(f.stat().st_size for f in storage.rglob("*") if f.is_file())
+        print(f"\nZotero storage size: {total_bytes / 1024 / 1024:.1f} MB")
+
+    con.close()
+    print("\nTo retrieve PDFs: open Zotero, select 'Skin Substitutes' collection,")
+    print("select all items (Ctrl+A), right-click → Find Available PDF.")
+    print("scipdf plugin (v8.0.4) will try Unpaywall then 7 SciHub mirrors.")
+
+
+if __name__ == "__main__":
+    main()