Reduce MediaWiki log level to "error" to minimize disk usage

Summary:
MediaWiki logs all levels by default (from debug to emergency), which generates
excessive noise and consumes unnecessary disk space. This change sets the log
level to "error", significantly reducing verbosity.

Reasoning:

The "warning" level is still too verbose.
For example, it logs expected cache hits and misses.

Reducing to "error" keeps logs focused on actual issues.

Initial configuration date: 2025-02-11

Test Plan:
Tested on web-001 (applied during an emergency situation).

Logging was stable and concise, with only 117 lines recorded. These were all relevant:

• Two missing thumbnails for Wolfplex wiki
• Connection timeouts with Wikimedia Commons

Reviewers: DorianWinty

Reviewed By: DorianWinty

Differential Revision: https://devcentral.nasqueron.org/D3709