* feat(plugins): add PluginContext and lifecycle type definitions * feat(validation): add Zod schema for plugin.json manifest * feat(db): add plugins, plugin_settings, plugin_permissions schema * feat(plugins): add PluginContext factory with scoped cache and settings Factory function createPluginContext() that builds a sandboxed PluginContext with key-prefixed cache, read-only settings wrapper, scoped database access, and child logger. Cache is only provided when the plugin has cache:read or cache:write permissions. * feat(plugins): add plugin loader with discovery, validation, and DB sync Implements topological sort for dependency ordering, manifest validation with filtering of invalid/missing-dep plugins, filesystem discovery of @barazo/plugin-* and barazo-plugin-* packages, and database upsert for discovered plugins (new plugins inserted as disabled). * feat(validation): add admin plugin settings and install schemas * feat(routes): add admin plugin management API routes * feat(db): add migration for plugin tables * feat(app): register plugin routes and startup discovery * fix: update lockfile for @singi-labs/lexicons rename