fix(gateway): respect explicit plugin platform disable

[applerom]

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

[teknium1]

Thanks for the focused gateway regression fix. This is now implemented on current main; this automated hermes-sweeper review found the PR redundant.

• gateway/config.py:2156 skips registry auto-enablement when a platform is both disabled and explicitly configured as such, so check_fn() / is_connected() cannot reactivate it.
• gateway/config.py:1125 records explicit enabled provenance with _enabled_explicit; this preserves auto-enable for default enabled=False values while honoring user intent.
• Commit 5600105478ffde29d7566b45421b100eaa29c4ef carried this behavior into the bundled-platform migration and shipped in v2026.7.1.

The linked issue discussion for #31049 also records the broader plugin auto-enable/reconnect behavior as resolved on main.