fix: override vulnerable protobufjs dependency

[Pigbibi]

Summary

• pin transitive protobufjs to 7.6.5 through npm overrides
• resolve the Dependabot advisory that cannot be updated automatically because of its dependency graph

Validation

• npm install --package-lock-only --ignore-scripts
• verified every locked protobufjs package resolves to 7.6.5
• npm ci --ignore-scripts
• node --check main.js
• node tests/test_auth_code_extraction.js
• node tests/test_proxy_config.js
• bash tests/test_workflow_config_sources.sh

No token-refresh runtime workflow was invoked.