Reduce logging verbosity in PDF preview endpoint

[cbcoutinho]

Problem

Every PDF preview request logs at INFO level (lines 682, 687, 781 in visualization.py):

logger.info(f"PDF preview request: file_path={file_path_param}, page={page_param}")
logger.info(f"PDF preview authenticated for user: {user_id}")
logger.info(f"Rendered PDF preview: {file_path} page {page_num}/{total_pages}, {len(png_bytes):,} bytes")

In production with many users, this creates excessive log noise.

Recommendation

• Change lines 682, 687 to logger.debug()
• Keep line 781 as logger.info() but consider sampling or only logging on errors

Location

• nextcloud_mcp_server/api/visualization.py:682, 687, 781

Priority

Recommended - Should fix for production environments

Parent Issue

Part of #502