feat(storage): inline preview for json/csv/log/text files

Add a /preview endpoint that range-reads the first chunk of an object and
returns it as text. Browser gets an eye action (list + gallery) opening a
modal that pretty-prints JSON, renders CSV/TSV as a table, and shows logs/
text/yaml/xml verbatim, with a truncation note and download link.

api/storage_s3.py

@@ -257,6 +257,39 @@ async def download_object(bucket: str, key: str = Query(...), inline: bool = Que
         return JSONResponse({"ok": False, "error": str(exc)}, status_code=404)
 
 
+@router.get("/buckets/{bucket}/preview")
+async def preview_object(bucket: str, key: str = Query(...), max_bytes: int = Query(131072, le=1048576)):
+    """Return the first chunk of an object as text for inline preview."""
+    try:
+        _track("preview")
+        s3 = _client()
+        head = None
+        try:
+            head = s3.head_object(Bucket=bucket, Key=key)
+        except Exception:
+            pass
+        total = int(head.get("ContentLength", 0)) if head else 0
+        obj = s3.get_object(Bucket=bucket, Key=key, Range=f"bytes=0-{max_bytes - 1}")
+        raw = obj["Body"].read()
+        truncated = (total > len(raw)) or (len(raw) >= max_bytes)
+        text = raw.decode("utf-8", errors="replace")
+        return {
+            "ok": True,
+            "bucket": bucket,
+            "key": key,
+            "ext": _ext(key),
+            "size": total or len(raw),
+            "size_human": _human_size(total or len(raw)),
+            "bytes_read": len(raw),
+            "truncated": truncated,
+            "content": text,
+        }
+    except ClientError as exc:
+        return JSONResponse({"ok": False, "error": str(exc)}, status_code=404)
+    except Exception as exc:
+        return JSONResponse({"ok": False, "error": str(exc)}, status_code=502)
+
+
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