Global log max-size settings should cap accepted byte/MB values

[Widthdom]

Finding

Global log retention count is clamped, but max-size environment and CLI values are only checked for being positive. Very large values can effectively disable rotation or allow unexpectedly large log files.

Evidence

• src/CodeIndex/Cli/GlobalToolLog.cs:634 clamps retain count to 1..10000.
• src/CodeIndex/Cli/GlobalToolLog.cs:638 accepts any positive CDIDX_LOG_MAX_SIZE_MB int and multiplies it by MiB.
• src/CodeIndex/Cli/GlobalToolLog.cs:640 accepts any positive CDIDX_GLOBAL_TOOL_LOG_MAX_BYTES long.
• src/CodeIndex/Cli/ProgramRunner.cs:612 validates --log-max-size-mb as positive but does not cap it.

Suggested fix

Add a documented maximum log size, clamp or reject larger CLI/environment values consistently, and cover both MB and bytes inputs in tests.

[Widthdom]

Work started on branch fix-issue2916-2915-2890-2889.