fix(environment): scope DeleteEnvironment lookups to current team

Scope DeleteEnvironment::mount() and delete() lookups through
Environment::ownedByCurrentTeam() so an environment_id that belongs to
another team resolves to a 404 instead of loading the foreign record.
Mark $environment_id as #[Locked] so the public Livewire property can no
longer be reassigned from the client.

Add tests/Feature/DeleteEnvironmentTeamScopingTest.php covering mount,
delete, the #[Locked] guard, and the team-scoped helper for both the
cross-team and own-team cases.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>