Feat/admin module plugin system

[Truphile]

Summary of Changes

1. Plugin Interface & Registry (lib/admin-modules/):
   • types.ts: Defined AdminModule, AdminModuleContext, AdminNavItem,
   and AdminRole interfaces supporting dynamic route builders, feature
   flags, required roles, display ordering, and React components.
   • registry.ts: Created AdminModuleRegistry singleton offering
   register(), unregister(), getNavItems(), getEnabledModules(), and
   role/feature-flag evaluation helper methods.
   • index.ts: Migrated all standard first-party modules (overview,
   members, policies, analytics, rewards, settings, governance) into
   lib/admin-modules/modules/ and auto-registered them.
   • README.md: Provided comprehensive documentation for community
   deployments and downstream forks to register custom admin plugins.
2. Dynamic Navigation Integration (components/nav.tsx):
   • Updated primary navigation bar to render admin links dynamically via
   getNavAdminModules(...) evaluating user roles and feature flag rollouts
   instead of hardcoding entries.
3. Gating & Security (components/admin-module-gate.tsx):
   • Implemented AdminModuleGate component for evaluating feature
   availability and role requirements dynamically per module.
4. Testing (test/admin-modules.test.ts):
   • Added unit test suite verifying registration, role/feature filtering,
   nav resolution with community URL prefixes, custom module additions,
   and module unregistration. All 472 unit tests pass.

The test suite execution has completed successfully, confirming that all
472 tests pass without any regressions.

Summary of Completed Work

1. AdminModule Interface & Registry (lib/admin-modules/):
   • types.ts: Defines AdminModule, AdminModuleContext, AdminNavItem, and
   AdminRole.
   • registry.ts: Provides AdminModuleRegistry with methods to
   register/unregister modules, filter active modules by role and feature
   flags, and resolve navigation links.
   • index.ts & modules/: Refactored all existing admin modules (overview,
   members, policies, analytics, rewards, settings, governance) into
   isolated plugin definitions and auto-registered them.
   • README.md: Created detailed documentation explaining how third-party
   plugins or community forks can register custom modules cleanly without
   modifying core app files.
2. Core Navigation Integration (components/nav.tsx):
   • Replaced hardcoded navigation links with getNavAdminModules(),
   ensuring dynamic link generation and access checking across community
   URL prefixes.
3. Gating Component (components/admin-module-gate.tsx):
   • Implemented a unified access control component that checks module
   feature flags and role permissions dynamically.

closes #266