feat: add flexible capability-based RBAC with per-tenant customization

Introduces a capability layer on top of existing roles that controls
feature visibility and access. Capabilities follow an area.feature.action
taxonomy (~35 capabilities) with sensible defaults per role. Tenant admins
can customize via grant/revoke overrides stored in org settings JSONB.

Key changes:
- Add vice_president role to DB schema
- Backend: capability constants, resolution logic, CapabilityGuard (global),
  @RequireCapability decorator on all 16 tenant controllers
- Frontend: permission hooks (useCanEdit, useHasCapability), CapabilityGate
  component, sidebar filtering by capability, all 17 pages migrated from
  useIsReadOnly to capability-based checks
- New admin UI: /settings/permissions matrix page for per-tenant role
  customization with grant/revoke delta model
- GET /organizations/my-capabilities endpoint for capability refresh
- Validation of permissionOverrides in settings updates

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/stores/authStore.ts

@@ -8,6 +8,7 @@ interface Organization {
   status?: string;
   planLevel?: string;
   settings?: Record<string, any>;
+  capabilities?: string[];
 }
 
 interface User {
@@ -119,7 +120,7 @@ export const useAuthStore = create<AuthState>()(
     }),
     {
       name: 'ledgeriq-auth',
-      version: 5,
+      version: 6,
       migrate: () => ({
         token: null,
         user: null,