add S3 browser section to bib_explorer notebook

refs #94

New section 10 connects to the zotero S3 bucket via s3fs and lists
files synced from Zotero through the WebDAV-to-S3 bridge. Shows
both the bucket root and the zotero/zotero/ sync directory.

notebooks/bib_explorer.py

@@ -716,6 +716,95 @@ def _(library_df, mo):
     return
 
 
+@app.cell(hide_code=True)
+def _(mo):
+    mo.md("""
+    ## 10. Zotero WebDAV Storage (S3)
+
+    Browse files synced from Zotero to the WebDAV-backed S3 bucket.
+    The `webdav` service (rclone) serves the `zotero` bucket in RustFS.
+    """)
+    return
+
+
+@app.cell(hide_code=True)
+def _(mo):
+    import os
+    import s3fs
+
+    _endpoint = os.environ.get("S3_ENDPOINT", "http://rustfs:9000")
+    _key = os.environ.get("RUSTFS_ACCESS_KEY", "")
+    _secret = os.environ.get("RUSTFS_SECRET_KEY", "")
+
+    fs = s3fs.S3FileSystem(
+        key=_key,
+        secret=_secret,
+        endpoint_url=_endpoint,
+        client_kwargs={"region_name": "us-east-1"},
+    )
+
+    try:
+        _files = fs.ls("zotero/", detail=True)
+        _rows = [
+            {
+                "path": f["Key"].removeprefix("zotero/"),
+                "size_kb": round(f.get("size", f.get("Size", 0)) / 1024, 1),
+                "modified": str(f.get("LastModified", "")),
+            }
+            for f in _files
+            if f.get("type", f.get("StorageClass", "")) != "directory"
+        ]
+    except Exception as e:
+        _rows = []
+        mo.md(f"Could not list S3 bucket: `{e}`")
+
+    import polars as _pl
+
+    s3_df = _pl.DataFrame(_rows) if _rows else _pl.DataFrame()
+
+    if s3_df.height > 0:
+        mo.md(f"**{s3_df.height}** files in `s3://zotero/`")
+    else:
+        mo.md("No files in `s3://zotero/` yet. Sync from Zotero to populate.")
+
+    return (fs, s3_df)
+
+
+@app.cell(hide_code=True)
+def _(mo, s3_df):
+    mo.ui.table(s3_df, label="Zotero S3 Files") if s3_df.height > 0 else mo.md("")
+    return
+
+
+@app.cell(hide_code=True)
+def _(fs, mo):
+    _zotero_dir = []
+    try:
+        _zotero_dir = fs.ls("zotero/zotero/", detail=True)
+    except Exception:
+        pass
+
+    _sync_rows = [
+        {
+            "file": f["Key"].removeprefix("zotero/zotero/"),
+            "size_kb": round(f.get("size", f.get("Size", 0)) / 1024, 1),
+        }
+        for f in _zotero_dir
+        if f.get("type", f.get("StorageClass", "")) != "directory"
+    ]
+
+    import polars as _pl
+
+    _sync_df = _pl.DataFrame(_sync_rows) if _sync_rows else _pl.DataFrame()
+
+    if _sync_df.height > 0:
+        mo.md(f"### Zotero Sync Directory\n\n**{_sync_df.height}** synced items")
+        mo.ui.table(_sync_df, label="Synced Files")
+    else:
+        mo.md("No synced files in `zotero/zotero/` yet.")
+    return
+
+
 @app.cell(hide_code=True)
 def _(mo):
     mo.md("""