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/permissions/useCapability.ts

@@ -0,0 +1,44 @@
+import { useAuthStore } from '../stores/authStore';
+
+/**
+ * Check if the current user has a specific capability.
+ * Superadmins always return true.
+ */
+export function useHasCapability(capability: string): boolean {
+  const user = useAuthStore((s) => s.user);
+  const capabilities = useAuthStore((s) => s.currentOrg?.capabilities);
+  if (user?.isSuperadmin) return true;
+  return capabilities?.includes(capability) ?? false;
+}
+
+/**
+ * Check if the current user has ANY of the given capabilities.
+ * Superadmins always return true.
+ */
+export function useHasAnyCapability(...caps: string[]): boolean {
+  const user = useAuthStore((s) => s.user);
+  const capabilities = useAuthStore((s) => s.currentOrg?.capabilities);
+  if (user?.isSuperadmin) return true;
+  if (!capabilities) return false;
+  return caps.some((c) => capabilities.includes(c));
+}
+
+/**
+ * Check if the current user has ALL of the given capabilities.
+ * Superadmins always return true.
+ */
+export function useHasAllCapabilities(...caps: string[]): boolean {
+  const user = useAuthStore((s) => s.user);
+  const capabilities = useAuthStore((s) => s.currentOrg?.capabilities);
+  if (user?.isSuperadmin) return true;
+  if (!capabilities) return false;
+  return caps.every((c) => capabilities.includes(c));
+}
+
+/**
+ * Check if a specific capability string matches the user's capability for edit actions.
+ * This replaces the old useIsReadOnly() for more granular checks.
+ */
+export function useCanEdit(editCapability: string): boolean {
+  return useHasCapability(editCapability);
+}