Add oxlint complexity rule

[karsten-bot]

Summary

• enable Oxlint’s built-in cyclomatic complexity rule with a maximum of 20
• avoid the JavaScript complexity plugin and its dependencies
• check every function, including short functions with dense branching

Verification

• built-in rule accepts complexity 20
• built-in rule reports complexity 21 with Maximum allowed is 20
• confirmed plugin configuration and dependencies are absent
• git diff --check

Linear: TIM-338