feat: enforce and preserve plugin configuration

[catherineluse]

Summary

• add a scope-aware plugin configuration status resolver
• hard-block plugin enablement when required settings or secrets are missing or invalid
• reconcile compatible settings when installing a new plugin version
• report carried, dropped, reset, and new-default fields
• preserve settings declared only through settingsDefaults

Why

Plugin configuration completeness was not represented consistently. Required non-secret settings could be bypassed during enablement, and upgrades reset per-version settings.

Validation

• 57 plugin-service tests
• TypeScript type-check
• ESLint on changed files

Implements the backend portion of gennit-project/multiforum-nuxt#330.

[codecov]

Codecov Report

❌ Patch coverage is 75.95745% with 113 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
customResolvers/queries/getPluginConfigStatus.ts	37.03%	51 Missing ⚠️
services/plugin/configStatus.ts	83.41%	33 Missing and 3 partials ⚠️
customResolvers/mutations/installPluginVersion.ts	75.47%	12 Missing and 1 partial ⚠️
customResolvers/mutations/enableServerPlugin.ts	66.66%	7 Missing ⚠️
services/plugin/reconcileSettings.ts	93.33%	6 Missing ⚠️

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