[ZhuchkaTriplesix]

Part of #1760 (error-handling epic #1764).

• QueryaLog (lib/core/util): timestamped LEVEL [area] message lines in <logs dir>/querya.log (SandboxLogPaths.logsDirectory, so portable mode stays portable), rotated by size (5 files of 2 MB). Writes are queued and ordered; logging never throws, and a file that cannot be written is reported on the console only. Lines logged before init are kept. Text goes through McpRedaction (URL user info, password=..., private keys).
• logIgnored, FlutterError.onError, the zone handler and the start-up failure write to it; debugPrint stays for the console.
• Tests: format, pre-init buffering, rotation, redaction, multi-line stacks, unusable directory, failing file.

Not in this PR (still open in #1760): Help menu Open logs folder and Copy diagnostics, and moving the remaining ~75 debugPrint calls. Not run locally, CI will.