fix: respect explicit plugin platform disables

[NicoMetaBreakThrough]

Fixes plugin platform disable handling so explicit platform disables are respected.

[alt-glitch]

Duplicate of #31596 — same fix for _apply_env_overrides() ignoring explicit enabled: false on plugin platforms. Previous duplicates: #31665, #31676, #32148.

[NicoMetaBreakThrough]

Thanks for pointing that out. I saw #31596 is currently conflicting, while this PR is mergeable against main. Happy to close this if maintainers prefer to continue with #31596, but leaving it open in case this is useful as a clean/current branch.

[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:1125 records _enabled_explicit for every platform block that explicitly sets enabled.
• gateway/config.py:2156 skips plugin-registry auto-enablement when that platform is explicitly disabled, so plugin checks cannot reactivate it.
• Commit 5600105478ffde29d7566b45421b100eaa29c4ef carried this behavior into the bundled-platform migration and shipped in v2026.7.1.

The member comment identifying #31596 as the canonical duplicate is consistent with the later implementation on main.