What does this PR do?

Fixes registry-driven gateway plugin platform activation so an explicit enabled: false configuration is respected even when plugin auto-detection would otherwise enable the platform.

Related Issue

Fixes #31049

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update
• Refactor
• Test update

Changes Made

• Respect explicit enabled: false for registry-driven plugin platforms during gateway env overrides.
• Preserve auto-enable behavior when a plugin platform has no explicit disable and its check_fn() passes.
• Add regression coverage for both explicit-disable and default auto-enable paths.

How to Test

• scripts/run_tests.sh tests/gateway/test_plugin_platform_explicit_disable.py — 2 passed
• python -m pytest tests/gateway/test_bluebubbles.py tests/gateway/test_whatsapp_group_gating.py tests/gateway/test_plugin_platform_explicit_disable.py -q -o 'addopts=' — 77 passed

Tested Platforms

• Linux / Hermes VM

Reviewer Notes

Pre-PR review was run through Hermes review-agent and OpenCode reviewers. No blocking findings remained; draft PR opened to let upstream CI and maintainers review.

Checklist

• I have read the contributing guidelines
• My commits follow the Conventional Commits format
• I have added tests for the bug fix
• I have run the relevant tests locally
• This PR focuses on one logical change