[Proposal] Create `plugin-setup` to own and finalize the platform Setup App

[hotlong]

Proposal: Add plugin-setup to Own and Register the Platform Setup App

Background

• Currently, setup app (系统设置/Setup) is dynamically composed by the engine, with its title, icon, i18n, default branding, and area skeletons (Administration, Platform, System, AI, etc) scattered in either objectql or spec.
• It is unclear where the platform Setup App's authority (as an app), lifecycle, and registrations should reside. This creates architectural confusion: protocol and data engine (spec, objectql) should not own system-level app instances or finalize navigation merges.
• All other major system entities (e.g., users, roles, audit logs) are owned by internal plugins: plugin-auth (SysUser), plugin-security (SysRole), plugin-audit (SysAuditLog), etc.

Proposal

• Create a dedicated plugin-setup (e.g. packages/plugins/plugin-setup) as a first-class internal platform plugin, sibling to plugin-auth and plugin-security.
• This plugin should:
  • Export Setup App identity: name, label (multi-lang), icon, permissions, branding, and all default meta.
  • Contain the 4 built-in Setup Areas (Administration, Platform, System, AI) as empty group skeletons for other plugins to contribute their settings/navigation.
  • On kernel/engine ready/finalize, collect all setupNav contributions, merge areas and groups, filter out empty areas, and register the finalized Setup App as an internal platform app.
  • Optionally: define platform Setup Home page, handle global Setup search, enforce Setup permissions.
• Remove all platform Setup App definition and merge logic from objectql and spec, making those packages protocol- and data-focused only.

Benefits

• Architectural clarity: spec = protocol only, objectql = data/query only, plugins = system feature and UI composition.
• Matches existing extensibility model: all system apps and objects are owned by plugins for encapsulation, modularity, and clear ownership.
• Greatly simplifies cross-repo and downstream system extension.
• Foundation for future features: Setup as a visible app, plugin-aware Setup Home, Setup extensibility via plugin-contributed areas/pages/search.